In order to clarify the effect of storage temperature on the freeze denaturation of fish protein, myosin B solutions in 0.6_M KCl prepared from six kinds of fish were frozen and stored at temper-atures in a range of -4 ?? -20°C. The apparent rate constants for the inactivation of myosin B Ca-ATPase (k_F) were calculated for comparison. The k_F value for each myosin B increased as the temperature decreased from -4 to -10°C, and reached a maximum in the range of -10 ?? -11°C. Since this temperature range was very close to the eutectic point of KCl (-11.1°C), it was suggested that the denaturation of myosin B during frozen storage is affected by the concentrated KCl solution yielded in the range above the eutectic point. The k_F values at each frozen-storage temperature differed in each fish