A seat height adjustment mechanism includes a locking bar and a locking element. The locking bar is disposed in a stroller frame and has locking holes spaced apart. Each of the locking holes has a stop portion protruding therein. The locking element is mounted on a seat and has an engaging end. The engaging end is separably engaged in any one of the locking holes and has an engaging hook protruding in a direction, and the direction is crossed with another direction in which the engaging end moves when the engaging end is separating from the locking hole. The engaging hook separably presses against the stop portion. Therefore, the engaging end cannot separate from the locking hole. Even when wrongly operated, the locking element cannot be rotated and unlocked and thereby prevents the seat from unnecessarily sliding downward, so as to ensure safety of a baby at the seat.