Abstract: Different temperatures heat treatment was carried out on annealing IF steel sheets and the influences of heat treatment temperatures on microstructure and mechanical properties of the IF steel sheets were studied.The results show that the carbonaceous secondary-phase particles distributed dispersedly in grains of the IF steel sheets.With the increase of heat treatment temperature,the amount of secondary-phase particles decreased,the yield strength and tensile strength of the steel increased,and the value of r (plastic strain ratio) and n (tensile strain hardening exponent) decreased.That is to say,the deep drawability of the IF steel sheets decreased with the increase of heat treatment temperature.