A rear suspension system of an automotive vehicle is disclosed. A trailing arm is disposed in a lengthwise direction of a vehicle body, and a mounting bush secures a leading end portion of the trailing arm to the vehicle body. A protrusion member protrudes from an outside circumference of the mounting bush. A coupling is provided on the leading end portion of the trailing arm, for making the length of the protrusion member varied in accordance with an external force imposed on the trailing arm. Thus, the wheel alignment is maintained at the tow-in during a braking or turning, and therefore, the vehicle posture is stabilized during the braking or turning.