USB serial driver for Windows
Windows includes a USB serial driver, Usbser.sys, which loads on its own for devices that use the USB communications class with subclass 02. Adapters built on chips such as CH340, FTDI, CP210x or PL2303 often use the chip maker's driver instead. Identify the chip from the hardware ID, then pick the matching driver.
Checked October 30, 2026 against the manufacturer's own pages.
Driver downloads
| Driver | Version | Released | Size | Windows | Download |
|---|---|---|---|---|---|
| Usbser.sys, included in Windows (no download needed) | See maker page | See maker page | See maker page | Windows 10 and 11 | Download from learn.microsoft.com |
Values copied from the manufacturer's page on October 30, 2026. The file always downloads from the manufacturer, never from this site.
The short version
What to install and where it comes from. Every link goes to the manufacturer or Microsoft, never to a copy.
Official files only, nothing bundled
Step by step
Plug it in and look at Ports
Open Device Manager and expand Ports (COM and LPT). A working serial device shows a name and a COM number.
Find the hardware ID
If it sits under Other devices, open Properties, Details, Hardware Ids. Note the VID and PID, for example VID_1A86 or VID_0403.
Let Windows try first
Run Windows Update and check Optional updates. For class devices Windows installs Usbser.sys without any download.
Match the vendor ID to a maker
1A86 points to WCH, 0403 to FTDI, 10C4 to Silicon Labs and 067B to Prolific. Use that maker's page only.
Check the cable
A cable that carries only power will never show a port. Try a second cable and another USB port before reinstalling anything.
Two kinds of USB serial adapter
A USB serial adapter makes a COM port that programs can open. There are two ways it gets its driver. One is the driver already in Windows. The other is a driver from the chip maker.
The first way applies to devices that follow the USB communications device class, known as CDC. Microsoft’s documentation explains that Usbser.inf sits in the Windows INF directory and loads Usbser.sys. The load happens by itself when the device reports class 02 and subclass 02. The device’s maker needs no INF of their own. Microsoft’s advice is to use the drivers included with Windows whenever possible.
Where the chip driver comes in
Plenty of cheap adapters use a vendor-specific design instead. Those need the chip maker’s driver to create the COM port. The four chips we cover are the common cases: CH340 from WCH, FTDI parts, Silicon Labs CP210x and Prolific PL2303. Each has its own page on this site, with the hardware IDs and the maker’s download.
How to tell which you have
Read the hardware ID in Device Manager. The vendor code is the key. The adapter may carry a brand name unrelated to the chip, but the ID does not change. Compare it with the four codes in the facts above. If it matches none, check the device maker, since some products use custom chips.
When the built-in driver loads but does not work
Class 02 with a subclass other than 02 will not load Usbser.sys on its own, and Windows may find no driver. In that case the device maker should provide an INF, or you may be told to use another in-box driver. Do not edit INF files by hand or turn off signature checks. Ask the maker for a package.
Questions
What is Usbser.sys?
It is the driver Microsoft ships for USB communications devices. Microsoft says to use drivers included with Windows whenever possible.
Why does my adapter need a different driver?
Many chips do not present themselves as a standard CDC device. They use their own protocol, so the chip maker writes the driver that makes the COM port.
Can I force Usbser.sys onto any device?
Not reliably. Microsoft says a device with class 02 but another subclass does not load Usbser.sys automatically. Use the maker's driver instead.
Where do I get a driver for an unknown serial adapter?
Read the hardware ID, find the chip maker from the vendor code, and download from that maker, or from the adapter's own brand.