Cognate mechanisms have been often used in design of linkages. Improper positions of fixed link or transmission angle could be improved effectively. Cognate mechanisms of planar linkages have been developed well, but the research on the spherical cognate is still wild open. There are just only spherical supplement mechanisms that have been presented by Soni(1967) until today. The aim of this thesis is to investigate the existence of spherical four-bar linkages cognate mechanisms. The geometry and properties of planar cognate mechanisms are discussed and a simulation program is written for the planar cognate mechanism. Then, the characteristics of spherical mechanisms are considered and the spherical cognate simulation program is built by using the result of planar cognate as a reference. Three examples are given to demonstrate the existence of pseudo-cognates for spherical mechanisms.