The sintered cemented tungsten carbite alloys having with binder phase, Co, are used that the materials for the tip of cutting tools and dieses. Then, surface of these tool parts are coated with ceramic thin film, i. e. titanium carbite, TiC, film and titanium nitride, TiN, film by physical vapor deposition, PVD, method or chemical vapor deposition, CVD, method. In recently, many researchers are estimated of physical properties and growth behavior that the diamond thin film was coated on the surface of various tools by thermal-filament CVD method. However, quite a few problems remain unsolved regarding the mechanical properties, it is important to know these properties of a diamond thin film on WC-Co alloys. This paper was mainly studied about the effect of diamond coating on fatigue strength of the sintered tungsten carbite alloys including with binder phase, Co, at 10, 16 and 25 wt.%. Then, the growth behavior and occurrence of thermal residual stresses of diamond film were evaluated by using for the Raman spectra analysis and X-ray diffraction method. As results, the fatigue strength of this material was depended on growth behavior and residual stress of diamond film.