To clarify the effect of Titanium Nitride (TIN) coatings on the failure resistance and frictional characteristic and compare this effect with that produced by the heat treated coatings@ two roller tests have been made and the stress resulting from the combination of the Hertzian stress field and frictional force field on and below zhe contacting surface as well as the flash temperature rise were calculated. The failure resistance of the TiN-coated roller pair was greater than that of the heat treated roller pair. The mechanism of failure resistance can be explained by the shearing stress (Hertzian stress + frictional force) acting on the contact surface. This stress modifies the structure in the vicinity below the TiN layer which is then sheared in the wear track direction.