To improve the lubricity of titanium nitride-titanium (TiN-Ti) composite in water, a hydrophilic silane coupling agent was added to the water. The tribological characteristics of the TiN-Ti composite in distilled water and in aqueous solutions of the silane coupling agent ranging in concentration from 0.001 to 0.1 mol/L were investigated. The silane coupling agent effectively inhibited the formation of a thick titanium oxide layer, which degrades the water lubricity of Ti-based materials, on the sliding surface. The lubricity of the TiN-Ti composite in the aqueous solutions of the silane coupling agent was much better than that in distilled water.