The main purpose of this paper is to use the concept of manipulability index for finding the optimal link lengths of a surgical robot and then to plan an optimal path for it. This index depends on the configuration of the robot. In each configuration, the manipulability of the robot is calculated thorough the Forward and Inverse Kinematic and Jacobain. In the present paper, a nonlinear constrained optimization problem is formulated based on this index to find the optimum link lengths. The optimization problem is solved using Genetics Algorithm for entire work space of the robot. The manipulability index is calculated all over the workspace using the Mont-Carlo method. Afterward, using this set of optimal link lengths, the optimal path planning is presented in the Cartesian work space. This optimization is done by considering the manipulability criteria while the tracking error is minimized during performing an operation. The suggested procedure is implemented on a four degree of freedom robot manipulator. Several simulations scenarios are presented to demonstrate the capability of the procedure. The simulation results show the efficiency of the method.