Disclosed is a seat post assembly for a human powered vehicle, the seat post assembly including a upper tube and a lower tube where the upper tube is telescopically received in the lower tube, the seat post assembly further including a nut holder tube, a nut, a motor and a lead screw, the motor is attached to the top of the upper tube, the nut holder tube is provided inside the lower tube, the nut is attached in a top portion of the nut holder tube, the lead screw is provided inside the upper tube and the nut holder tube and is with one of its ends attached to an axle of the motor, the seat post assembly is configured to raising or lowering the upper tube relative to the lower tube by rotating the lead screw in forward or backward direction respectively.