A PDS based bilateral control system of flexible master-slave arms with random delay is investigated in this paper. Moreover, a flexible slave arm employed in this research is affected by a contact force. A rigid master arm and a flexible slave arm which is actuated by a high-geared servomotor construct the proposed bilateral control system. Both arms are connected by a communication network. It is considered that this network occurs a random delay. Furthermore, the contact force is added to the flexible arm during its motion. Thus, the motion of this arm is restricted by the contact force. A Kalman filter is designed to estimate signals and controllers for both arms are designed as the PD-and PDS-controllers, respectively. Numerical simulations are achived to confirm the performance of the proposed system such as the instability of its motion and the adaptivity of the Kalman filter.