Content Summary : Recent advances in technology have led to the fusion of MIS techniques and robot devices. However, current systems are large and cumbersome. Optimizing the surgical robot mechanism will eventually lead to its integration into the operating room (OR) of the future becoming the extended presence of the surgeon and nurses in a room occupied by the patient alone. By optimizing a spherical mechanism using data collected in-vivo during MIS procedures, this study is focused on a bottom-up approach to developing a new class of surgical robotic arms while maximizing their performance and minimizing their size. The spherical mechanism is a rotational manipulator with all axes intersecting at the center of the sphere. Locating the rotation center of the mechanism at the MIS port makes this class of mechanism a suitable candidate for the first two links of a surgical robot for MIS. The required dexterous workspace (DWS) is defined as the region in which 95% of the tool motions are contained based on in-vivo measurements. The extended dexterous workspace (EDWS) is defined as the entire abdominal cavity reachable by a MIS instruments. The DWS is defined by a right circular cone with a vertex angle of 60º and the EDWS is defined by a cone with an elliptical cross section created by two orthogonal vertex angles of 60º and 90º. A compound function based on the mechanism’s isotropy and the mechanism stiffness was considered as the performance metric cost function. Optimization across both the DWS and the EDWS lead to a serial mechanism configuration with link length angles of 74º and 60º for a serial configuration This mechanism configuration maximized the kinematic performance in the DWS while keeping the EDWS as its reachable workspace