To back up a specific GPO, follow these steps:
Open the GPMC.
Expand the Forest and Domain trees in the left pane, and then select Group Policy Objects under your domain.
In the right pane, select the GPO you want to back up.
Right-click the GPO and select Back Up.
The Back Up Group Policy Object dialog box appears. Enter the location where you want to store the backed-up GPO files in the first box, and then enter a helpful description for yourself so that you can identify the backed-up files later.