This paper presents an approach for designing a novel coaxial indexing mechanism composed of conjugate cams and parallelogram linkage. Compared with the conventional indexing cam mechanisms, the mechanism has a more compact mechanical structure thanks to the coaxial input/output shaft arrangement, and produces higher number of stops at the same speed of input shaft. Firstly, on the basis of systematically describing the working principle of the mechanism, the conjugate cam profiles, curvature radius of cam profiles and meshing equation between the cam and roller are established. Then, the main factors affecting the geometric characteristic and the force transmission performance of the mechanism are analyzed. The dimensional synthesis of this mechanism is further researched. Finally, prototypes are developed and experiment is performed to verify the feasibility of the mechanism. The research provides a train of new thoughts for the mechanical design of indexing mechanisms.