A structure of seat cushion frame in a vehicle seat, which has a pair of upwardly projected side frames, one of them being disposed at the side of a door of the vehicle, wherein such one of the side frames is formed with a cut-away portion at the rearward are thereof, with a forward side frame being thus defined therein, and wherein an expandable member is extended between the cut-away portion and forward side frame. The expandable member acts to allow vertical flexture of the corresponding lateral bolster portion of seat cushion, after upholstering the seat cushion frame to form the seat cushion, so that a passenger can descend from or climb onto the seat with a comfortable touch.