Your USB-to-serial adapter suddenly stops working, or worse, your Windows 11 PC crashes with a Blue Screen. The culprit? A tiny but critical file called usb2ser.sys. This serial to USB driver, tucked away in your System32 folder, has become one of the most common sources of driver-related headaches for Windows 11 users. I've spent the better part of a decade helping users untangle this exact mess, and I can tell you this: the fix is usually simpler than you think.
In this guide, I'll walk you through five proven fixes for usb2ser.sys errors on Windows 11—from quick workarounds to permanent solutions. Whether you're staring at a "file missing" error, dealing with a BSOD, or locked out of Memory Integrity, I've got you covered. This guide is updated for the latest Windows 11 versions in 2026.
What is usb2ser.sys and Why Does It Cause Problems on Windows 11?
The Role of usb2ser.sys in Your System
Let's start with the basics. usb2ser.sys is a system driver file that enables USB Serial Adapters to communicate with your PC. It's most commonly associated with Prolific or MediaTek chipsets—those little dongles that let you connect older serial devices (think industrial equipment, routers, or even some phone debugging tools) to modern USB ports.
The file lives in C:\Windows\System32\drivers and loads during system startup. Here's a simplified view of where it sits in the driver stack:
Application (e.g., PuTTY, Device Manager)
↓
Windows API Layer
↓
usb2ser.sys (serial-to-USB bridge driver)
↓
USB Port Driver (usbhub.sys)
↓
Physical USB Port
Now, here's the thing that trips up a lot of users: usb2ser.sys is not a virus. It's a legitimate driver. But it's an old driver, and that's where the trouble begins.
Common Error Scenarios: Missing, BSOD, and Memory Integrity Conflicts
In my years of troubleshooting, I've seen three distinct failure modes with this driver:
1. "usb2ser.sys missing" or "Not Found" errors This typically happens after a Windows update or when the driver gets corrupted. The system expects the file to be there, but it's gone or unreadable.
2. Blue Screen of Death (BSOD)
The most common stop code is IRQL_NOT_LESS_OR_EQUAL. This usually means the driver tried to access memory at an invalid address—a classic sign of an outdated or buggy driver. I've also seen SYSTEM_THREAD_EXCEPTION_NOT_HANDLED with this file.
3. Memory Integrity disabled due to incompatible driver This is the one that confuses people the most. Windows 11's Core Isolation feature (specifically Memory Integrity) blocks drivers that don't meet modern security standards. usb2ser.sys, especially older versions, gets flagged because it doesn't support the required memory protection features.
The issue is particularly prevalent on OEM machines from Dell and HP, which often pre-install the driver even if you never use a serial device. I've lost count of how many users I've helped who had this driver sitting on their system for years without ever knowing it.
How to Fix usb2ser.sys Missing or Not Found Error in Windows 11
Method 1: Quick Fix – Disable the Driver via Device Manager
If you're in a hurry and just need the BSOD to stop, this is your fastest option. It's also the least invasive—you're not deleting anything, just telling Windows to leave the driver alone.
Step-by-step:
- Press
Win + Xand select Device Manager. - Click View in the menu bar and select Show hidden devices.
- Expand the Ports (COM & LPT) section. Look for "USB Serial Controller" or "Prolific USB-to-Serial Comm Port."
- Right-click the device and select Disable device.
- Confirm the warning dialog.
That's it. The BSOD should stop immediately, and you'll be able to enable Memory Integrity in Windows Security.
The catch: Your USB-to-serial adapter will stop working. If you actually use that hardware, this is only a temporary stopgap. But if you're like many users who never plugged anything into that port, this might be all you need.
Method 2: Advanced Fix – Permanently Remove the Driver with pnputil
This is the method I recommend most often. It's clean, it's thorough, and it removes the driver from the Windows driver store entirely—not just disables it.
Step-by-step:
- Right-click the Start button and select Windows Terminal (Admin) or Command Prompt (Admin).
- First, let's see what we're dealing with. Run this command to list all third-party drivers:
dism /online /get-drivers /format:table
-
Look through the output for anything related to usb2ser.sys. You'll see a "Published Name" like
oem25.inf. Write this down—you'll need it for the next step. -
Now, delete the driver package:
pnputil /delete-driver oem25.inf /uninstall /force
Replace oem25.inf with the actual published name you found.
- Restart your PC.
After the restart, the driver should be completely gone. You can verify by running the dism command again and checking that the entry is no longer there.
A word of caution: If you get an "Access denied" error, make sure you're running the terminal as Administrator. I've seen this trip up more than a few users—including some who were sure they had admin rights.
Method 3: Update usb2ser.sys to a Compatible Version
What if you actually need the serial device? Deleting the driver isn't an option. In that case, updating is the way to go.
Step-by-step:
-
Check Windows Update first. Go to Settings > Windows Update > Advanced options > Optional updates. Look for any driver updates listed there. Microsoft has been pushing signed, compatible versions of this driver through Windows Update.
-
Visit the OEM's website. If you have a Dell or HP machine, check their support pages. They often have custom-signed versions of the driver that work with Windows 11.
-
Go straight to the source. For Prolific chipsets, visit Prolific's official driver page [需核实链接有效性]. They've released Windows 11-compatible versions of their drivers.
-
Manual update via Device Manager: Right-click the device in Device Manager, select Update driver, then Browse my computer for drivers. Point it to the downloaded driver folder.
Important warning: You might see advice online about disabling "Driver Signature Enforcement" to install older drivers. I strongly advise against this. It weakens your system's security and can cause more problems than it solves. If a driver isn't signed for Windows 11, it's not worth forcing it.
Is It Safe to Delete usb2ser.sys? Risks and Side Effects Explained
What Happens After You Remove the Driver?
Let me be direct: deleting usb2ser.sys is safe if you do it the right way. But you need to understand the consequences.
| Before Removal | After Removal |
|---|---|
| USB-to-serial adapters work normally | USB-to-serial adapters stop functioning |
| Memory Integrity may be blocked | Memory Integrity can be enabled |
| Potential BSOD risk with old versions | BSOD risk eliminated |
| Driver appears in Device Manager | Driver disappears from Device Manager |
| The file won't be automatically recreated unless you reconnect the hardware and Windows reinstalls the driver. If you never use serial devices, you won't notice any difference. |
Before you proceed, create a system restore point. This is non-negotiable in my book. I've seen too many users skip this step and regret it later. Search for "Create a restore point" in the Start menu, and make one before making any system changes.
How to Backup and Restore usb2ser.sys
If you're not ready to say goodbye to the driver permanently, here's how to back it up:
- Navigate to
C:\Windows\System32\drivers. - Find
usb2ser.sys. - Copy it to a safe location (like a USB drive or your Documents folder).
To restore it later:
- Open Device Manager.
- Right-click the device and select Update driver.
- Choose Browse my computer for drivers.
- Click Let me pick from a list of available drivers on my computer.
- Click Have Disk, then browse to your backed-up file.
A critical warning: Never download usb2ser.sys from random websites. I've seen fake driver sites that bundle malware with "driver downloads." Always use official sources—Microsoft, the OEM, or the chipset manufacturer.
Preventing Future usb2ser.sys Errors: Best Practices for Windows 11
Keep Your Drivers Updated Automatically
The easiest way to avoid driver headaches is to let Windows handle it. Here's what I recommend:
- Go to Settings > Windows Update > Advanced options.
- Make sure Receive updates for other Microsoft products is turned on.
- Check Optional updates regularly—this is where driver updates often appear.
If you're considering a third-party driver updater tool, proceed with caution. Some are legitimate, but many are bloated with adware or make unnecessary changes. In most cases, Windows Update and the manufacturer's website are sufficient.
Understand Windows 11 Memory Integrity and Driver Compatibility
Memory Integrity is a security feature that prevents malicious code from accessing high-security system processes. It's part of Windows 11's Core Isolation framework, and it's genuinely valuable—it stops a whole class of attacks that exploit driver vulnerabilities.
The problem? Older drivers like usb2ser.sys weren't designed with these security requirements in mind. They use memory access patterns that Memory Integrity blocks, which is why Windows flags them as incompatible.
Here's my honest take: don't disable Memory Integrity just to use an old driver. The security trade-off isn't worth it. Instead, either update the driver or remove it. If you absolutely must use a serial device with an old driver, consider using a different adapter with a modern, compatible chipset.
FAQ
Is usb2ser.sys a virus or a safe file?
usb2ser.sys is a legitimate driver file from Prolific or MediaTek. It's not a virus. However, antivirus false positives can occur, especially with older versions. To verify authenticity, check the file's digital signature: right-click the file in C:\Windows\System32\drivers, select Properties, and look at the Digital Signatures tab. If it's signed by Microsoft Windows or Prolific, it's genuine.
How do I update the usb2ser.sys driver on Windows 11?
First, check Windows Update > Optional updates. If nothing's there, visit your PC manufacturer's website (Dell, HP, etc.) or the chipset manufacturer's site (Prolific). Download the latest signed driver, then use Device Manager > Update driver > Browse my computer to install it. Always use signed drivers from official sources.
Is it a good idea to turn off Memory Integrity to fix this error?
I don't recommend it. Memory Integrity is a core security feature that protects against sophisticated attacks. Disabling it leaves your system vulnerable. Instead, remove or update the incompatible driver. If you must disable it temporarily to test something, re-enable it as soon as possible.
Can I delete usb2ser.sys from System32 to fix the blue screen?
Manually deleting the file from System32 is not recommended. It can leave your system in an inconsistent state and may cause other issues. Use the proper removal methods—either Device Manager or the pnputil command—to uninstall the driver cleanly. See the "Advanced Fix" section above for the correct procedure.
Final Thoughts
Dealing with usb2ser.sys errors on Windows 11 comes down to three choices: disable it, remove it, or update it. Each has its place, depending on whether you actually use the serial device and how much you value Memory Integrity's security benefits.
In my experience, most users fall into one of two camps: those who never use the serial port and just want the error gone (remove it), and those who need the hardware for work or hobbies (update it). Both paths are straightforward if you follow the steps above.
One last piece of advice: always download drivers from official sources. I've seen too many horror stories from users who grabbed a "driver" from a sketchy website and ended up with malware. Stick with Microsoft, your OEM, or the chipset manufacturer, and you'll be fine.
If you found this guide helpful, share it with someone who might be struggling with the same issue. For more Windows 11 troubleshooting tips, subscribe to our newsletter or leave a comment below with your specific error code—I read every one and try to respond with personalized advice.