The effect of copper (Cu) addition on the grain growth behavior of austenite was investigated in a low carbon steel and a Cu bearing low carbon steel. Cu addition to the steel does not affect the nucleation rate of reversed austenite on heating in the martensitic structure but markedly retards the grain growth of the austenite during holding at 1173K (austenitization). As a result, the grain size of austenite in the Cu bearing steel becomes about one-third times smaller than that in the base steel after austenitization for 14.4ks. TEM observations in the Cu bearing steel revealed that Cu particles precipitated during aging treatment had completely dissolved in 1.2ks of austenitization. Therefore, the retardation of grain growth of austenite can not be explained by the grain boundary pinning effect of Cu particles but by the dragging effect of Cu atoms in the austenitic solid solution.