To investigate the effect of grain size on the core loss of non-oriented electrical steels, specimens containing various amount of Si were taken from commercially produced cold rolled sheets and annealed for grain growth. The annealing experiments were carried out in a double-stage mode in which the specimens were decarburized with wet H₂+N₂ atmosphere in the first stage and then annealed with dry atmosphere at various temperatures in the second stage. The core loss decreased initially and then increased along with the increased of grain size, therefore there existed an optimum grain size showing minimum value of core loss. It was also found that the optimum grain size is varying with the content of Si, such as 35㎛ at 0.81 wt%Si, 60㎛ at 2.13 wt%Si and 85 ㎛ at 3.20 wt%Si in this study. Since the texture coefficient of the specimens didn`t show any specific tendency on grain size, the behavior of core loss is considered to be mainly due to the grain size.