Abstract: Glow discharge ionized nickel chromizing with arc source was used to treat Ti5Al2.5Sn titanium alloy. The phases and constituent distribution in the treated surface were investigated by means of X ray diffraction and energy dispersive spectrometry. Shot peening was introduced to post treat the alloyed layer in order to synergically improve the fretting fatigue resistance of Ti alloy. The results show that a composite modified surface of NiCr coating over nickel chromium diffusion layer, which consists of N 3Ti and other phases, is formed on titanium alloy surface. Thus the hardness and wear resistance of titanium alloy are increased remarkably. As compared with the alloy subjected to shot peening alone, the titanium alloy after nickel chromizing and shot peening shows better fretting fatigue resistance. This is determined by the synergetic effect of the high wear resistance of the alloyed surface and the residual compressive stress induced by shot peening.