Provided is a socket for testing a main board having a water-cooled cooler fixing structure that fixes a water-cooled cooler to the top surface of a central processing unit (CPU) mounted to a main board for a computer during testing of the fraction defective of the main board. The socket for testing a main board includes a socket body having a size larger than a CPU mounted on a main board and having a cooler positioning recess of a predetermined size into which a water-cooled cooler is inserted to be positioned therein, the socket body being installed over the CPU mounted on the main board, a cooler fixing unit installed across an upper portion of the cooler positioning recess of the socket body, and having one end pivotally coupled to a top end of the socket body using a hinge to fix the water-cooled cooler inserted into and positioned in the cooler positioning recess, a cooler pressing unit, a bottom surface of which is attached to a top surface of the CPU mounted on the main board by resiliently pressing a top surface of the water-cooled cooler positioned in the cooler positioning recess of the socket body through fixation of the cooler fixing unit, and a socket fixing unit fixing the socket body onto the main board.