This paper presents the design of three-bar cam-link prosthetic knee mechanism using the instant centers of a natural knee measured experimentally obtained from literature. The cam in this mechanism is approximated as a nth order polynomial form. The instant centers generated by the mechanism are compared with those of the natural knee and the error is minimized using random search optimization techniques. Also, a tangents-merge method is used to develop the cam profile. Normals to the corresponding instant center radii of the cam are found and merged with suitable radii to get a continuous cam profile with no error at prescribed instant centers. The design gives a prosthesis with fewer links and greater accuracy. Results in the form of cam profiles, transmission angles and radius of curvatures are presented.