The prevalence of epidemic hepatitis at Kumayama-cho, Akayuwa-gun in Okayama prefecture was fully observed for 3 years and the epidemic transition was studied. And the results were as follows. 1. The prevalence of epidemic hepatitis diffusely distributed to each age showing the apex at the second decade and third decade, but it showed the low rate at the first decade. And it showed the percentage of contration with a little rise and fall in all ages at the first year and it changed to show the distribution of age distinction with the apex at the third decade and the similar wave at the second decade at the second year. These relation were explained by the immunological distoribution caused by the past prevalence. The contracted cases over 70 years old were not always few. 2. No fixed relation was not clarified on the sex distinction. 3. Studying the occured state of every month in each year and each district, the sporadic prevalence was only seen in each district at the begining of the prevalence and the seasonal feature was not seen at the first year of the prevalence, but the occurrence of epidemic hepatitis was mostly seen in July, August and September and it was rather numerous inMay, June and October at the second and third year. On the other word, the prevalence of epidemic hepatitis after the second year had a seasonal feature. 4. The recurrent rate of epidemic hepatitis was 13.94%, and the age with the frequent recurrence was at the second decade and then the third decade and the recurrent season was mostly seen in December, then June, July and October. On the other word, it was fit for the season at which time the resistence of physical strength became declined. 5. The infection rate of family was 42.83% (16-76%), and the member of occureence in same family was 2 members per one family in most of the cases and then 3 members. 6. The calculation of the incubation by the family infection was not proper and it was difficult to clarify the simultaneous infection, gradual infection or infection from the cutside of family.