Optimal design is one of the most important issues in robots. Since the very beginning, the concepts of the Jacobian matrix, manipulability and condition number, which are used successfully in the field of serial robots, have been applied to parallel robots. Unlike serial robots, parallel robots are good for motion/force transmission. Their performance evaluation and design should be correspondingly dif- ferent. This paper is an attempt to optimally design a novel spatial three-degree-of-freedom (3-DOF) parallel robot by using the concept of motion/force transmission. Accordingly, three indices are defined. The suggested indices are independent of any coordinate frame and could be applied to the analysis and design of a parallel robot whose singularities can be identified wholly by using the relative angle between the output and adjacent links, and by using the relative angle between the input and adjacent links. Opti the design is one of the most important issues in robots. Since the very beginning, the concepts of the Jacobian matrix, manipulability and condition number, which are used successfully in the field of serial robots, have been applied to parallel robots. Unlike serial robots , parallel robots are good for motion / force transmission. Their performance evaluation and design should be correspondingly dif- ferent. This paper is an attempt to optimally design a novel spatial three-degree-of-freedom (3-DOF) parallel robot by using The concept indices are independent of any coordinate frame and could be applied to the analysis and design of a parallel robot whose singularities can be identified entirely by using the relative angle between the output and adjacent links, and by using the relative angle between the input and adjacent links.