It is generally known that stress and strain relation is affected by strain rate and temperature. Constitutive relation between stress, strain, strain rate and temperature is very important to make clear the problem acting on dynamic load. Then many constitutive equations have been proposed by many researchers. In the previous paper, we suggested the constitutive equation for mild steel can be presented as a function of strain rate-temperature parameter ( R ). It is in good agreement with experimental data. But we need to carry out many round bar tension tests if we want to estimate constitutive equations for other structural steels. In this paper, we investigate the simple method to decide on the material constants for estimating constitutive equation by using our suggested method. In this method, we can easily decide on the material constants if only the yield stress under quasi-static condition at room temperature (20°C) is given. Then we try to estimate constitutive equations for cases of mild steel and HT-80 steel at various strain rates and temperatures. As a result, it becomes clear that we can get easily constitutive equations for arbitrary structural steels if only the yield stress under quasi-static condition at room temperature (20°C) is given.