A circuit board is for inserting an expansion card with a positioning part. The circuit board includes a board body, a slot, a release assembly, and a transmission mechanism. The release assembly includes a release body, a blocking member, and an elastic member connected between the release body and the blocking member. The release body includes a blocking part for limiting the positioning part. The transmission mechanism includes a linkage part and a force applying part. When the force applying part receives an external force, the linkage part moves to move the release assembly toward a first direction, the elastic member returns to an original position to drive the blocking member to push against the positioning part to move out of the blocking part and to be located at a release position continuously, so as to release the limit of the positioning part by the blocking part.