A fastening structure for an expansion card has a pair of blocks disposed in a case. Each block has a slit, and each slit is facing and parallel to the slit on the other block. When fastening the expansion card, two opposite sides of the expansion card may be engaged into the opening of the pair of slits. At least a locking tab having a dent is disposed on one block and may rotate around the block. When the locking tab rotates, the dent and the slit may be selectively aligned or misaligned. When the dent and the slit are aligned, they may form a continuous passage for a side of the expansion card slitting into. Or when they are misaligned, the sidewall of the dent may block up the slit.