An unlocked-state retention device is adapted for use in a seat assembly. The seat assembly includes a base frame and a seat body, which is mounted removably on the base frame through a locking unit to lock or unlock the seat body relative to the base frame such that the seat body is placed in a locked state or an unlocked state. The unlocked-state retention device includes a pusher adapted to be disposed movably in one of the base frame and the seat body, and includes a push member to retract ably project from the one of the base frame and the seat body and to push the other one of the base frame and the seat body when the seat body is unlocked relative to the base frame.