Blood catalase level in healthy rabbits was measured before and after thermal bath of Misasa in January, May, July and September. And the differences in the effect of thermal bath between the four seasons were investigated. Blood catalase level in rabbits proved to be highest in winter and lowest in September. A slight fall in blood catalase level was recognized an hour after the thermal bath at 42℃ for five minutes. And in September the degree of fall seemed to be slightest and the recovery soonest.