Abstract: The effect of serpentine natural mineral powder as a lubricating oil additive on the friction and wear of tin bronze was investigated by using a SRV sliding wear tester. Scanning electron microscope, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and nanoindentation tester were employed to determine the elemental composition, chemical state, and nano mechanical properties of the worn surfaces. The friction reducing and lubricating mechanism of the serpentine additive was discussed. Results show that a tribofilm composed of metal oxides, oxide ceramic particles, graphite, and organics was formed on the tin bronze worn surfaces lubricated with oil containing the serpentine mineral. The nano-hardness and elastic modulus of the film demonstrated the gradient variation that low in the surface and high in the subsurface, as contributed to the improvement of the tribological behaviors of tin bronze.