This paper proposes a design of seat mechanism for multi-posture-controllable wheelchair to change seating posture into standing, reclining, tilting and elevation. The seat is designed based on a link mechanism including linear actuator and kinematics analysis. To control the multi-postures, we designed a Proportional–Integral–Derivative (PID)-based position and speed controller. In addition a motion planner is introduced to generate an available new posture. Simulation results showed that the designed seat mechanism and its motion planner are effective in developing the multi-postures-controllable wheelchair.