A motor assembly for starting an engine and driving a balance shaft may include: a motor for rotating a motor shaft which is axially movable; a clutch attached to one end of the motor shaft so as to transfer or block rotational force of the motor shaft; a balance shaft rotated by the rotational force of the motor shaft transferred through the clutch so as to reduce vibration generated by an engine; a start gear attached to the other end of the motor shaft; and an actuator for axially moving the motor shaft in a forward or backward direction.
