The crevice corrosion resistance of corn m ercially pure titanium and Ti-0.3% Mo 0.8% Ni alloy in boiling 25% NaCl and HCl solution was studied with electrochemical techniques. The results indicated that the Ti-0.3% Mo-0.8% Ni alloy have much better crevice corrosion resistance than commercially pure titanium. It is mainly related with the low hydrogen overpotential of the nickel which promoted the cathode polarization, increased the passivation ability. The nickel enriched in the internal crevice surface enhanced. the stability of passive film.