Abstract: Using polyvinylpyrrolidone (PVP) as a coupling agent, tetrabutyl orthotitanate (TBOT) as the precursor of titanium dioxide, and ammonia as catalyst, the ultrafine diamond coated with titanium dioxide (UFD@TiO₂) with core-shell structure was prepared by Stöber method. The influences of the pH value of the solution and the additions of ammonia and deionized water on the formation of UFD@TiO₂ were studied. The phase composition, microphotograph and oxidation resistance of UFD@TiO₂ were characterized by XRD, SEM and DSC-TG. The flexural strength of specimens of UFD-vitrified bond and UFD@TiO₂-vitrified bond was tested by three point bending method. The fracture micro-morphologies of vitrified bond specimens were observed by SEM. Results showed that when the pH value was approximately 8 and the volume fractions of ammonia and deionized water were both 0.8%, TiO₂ was heterogeneously nucleated on the surface of diamond with TBOT hydrolysis, evenly forming a dense layer of TiO₂ film. The initial oxidation temperature of UFD@TiO₂ was 650℃, which was 67℃ higher than that of the UFD. The flexural strength of UFD@TiO₂-vitrified bond specimen was 20.9% higher than that of UFD-vitrified bond specimens.