In this paper, a novel performance index is introduced for the kinematics optimization of serial robot manipulators. The serial robot manipulators used in order to compare optimization results were classified as in . The new performance index is a combination of a manipulability measure and condition number used by previous authors. To find the optimum link lengths and volumes of these robot manipulators, two design objectives are used: maximize the workspace area covered by the robot manipulator and maximize the new local index. As examples, two spherical three-link robot manipulators are examined based on above design objectives. Finally, optimization results of these robot manipulators are obtained and compared to each other.