We　reported　a　low-friction　performance　of　Ti-doped　a-C　film,　which　is　Ti-inducing　sp2　nanocrystallites　embedded　in　a-C　structure.　Mechanical　and　tribological　tests　showed　that　Ti-inducing　sp2　nanocrystallites　softened　the　film　hardness　from　22.5　to　18.8　GPa　and　lowered　the　friction　coefficient　from　0.15　to　0.05.　Friction　interface　char-acterization　indicated　that　abundant　sp2　nanocrystallites　lay　down　on　the　contact　surfaces.　The　low-friction　was　attributed　to　the　interaction　between　sp2　C　layers,　which　originated　from　original　Ti-inducing　and　new　Ti　-promoting　sp2　nanocrystallites.　The　Ti-promoting　effect　was　speculated　that　Ti　atoms　with　Ti-C　bond　reacted　with　O　atoms　to　form　Ti--O　bond　(TiO2),　then　some　released　C　atoms　turned　to　sp2　nanocrystallites　at　the　friction　interface.