The effects of temperature,stress and grain size on stress relaxation in the alloy TC4 have been investigated.The results show that;? the stress relaxation is sensitive to microstructure and test conditions;? increasing temperature results in higher stress relaxation rate and low relaxation limitation; ? change of initial stress also influences the stress relaxation rate and relaxation linitation; ? the fine- grain alloy has a higher stress relaxation rate than does the large- grain alloy.