Bilateral teleoperation is expected to be a key technology for the next generation of robots. Recently, four channel bilateral structures based on acceleration control have been introduced to realize both position and force tracking. Additionally, torque observers have been implemented to enable force feedback without sensors. However, when extended to the case of redundant manipulators, such joint space based control schemes show some limitations due to the use of the inverse Jacobian matrix. In order to address this issue, a workspace based bilateral control structure is proposed. In other words, the joint torque reference is synthesized by using the equivalent mass matrix without computing the inverse kinematics. The originality of the proposed approach lies in the design of a workspace force observer that equivalently estimates the reaction force in Cartesian space. Experimental results are provided to show the efficiency of the proposed workspace based bilateral control.