An MDPS (Motor Driven Power Steering) system may include: a vehicle speed sensor configured to sense vehicle speed; a yaw rate sensor configured to sense a tilted state of the vehicle, and output a yaw rate value; a lateral acceleration sensor configured to sense lateral acceleration which acts in a lateral direction of the vehicle; and an MDPS controller configured to receive the vehicle speed, the yaw rate value and the lateral acceleration from the vehicle speed sensor, the yaw rate sensor and the lateral acceleration sensor, respectively, and calculate assist torque by estimating column torque.