A seat frame reinforcement structure has a reinforcing member that is provided between both side frames that constitute a framework of a seatback of a vehicle seat, is connected to the side frames, and extends in the width direction of the vehicle seat. The reinforcing member includes a rod that is larger in diameter than each of operation pins that pass through center portions of reclining mechanisms, bushings that are connected to respective end portions of the rod, and a guide member that is connected integrally to the side frame so as to surround the outer periphery of a portion of the operation pin, which is exposed due to a clearance formed between an end portion of one of the bushings and the side frame. Due to the provision of the guide member, the diameter of the reinforcing member is maintained large even in a region where there is the clearance.