During matching process of the non-circular gear pair with cycloidal profile (epicycloid – hypocycloid), the profiles of the driving and driven gears are mating following the gearing principle of the non-circular gear train. Those profiles are generated by each other, and they will be rolling and sliding when working, producing a relative sliding velocity at the contact point. It is one of the factors causing the irregular wear of the mating gear-profiles. The sliding coefficient has been used to access this phenomenon when designing gear-train. Therefore, it is vitally necessary to set up analytical formulas to analyze, evaluate profile sliding process, and it is the goal of this research. Moreover, the achieved results also show that the combination of the epicycloid and hypocycloid profiles has an advantage over the involute profiles, because the sliding curve of the firstly mentioned profiles stays consistently symmetrical, which means both mating profiles are equally worn, and no adjusting of the sliding coefficient is required.
