Because of the cases of Japanese Encephalitis(J.E.) were reported every year in Korea. We, Dong-A Pharmaceutical Co., Ltd., produced J.E. virus vaccine, with lower price, since 1970 in order to prevent ourselves from being infected by the disease. And inoculated the J.E. virus vaccine for the children with a great success. We are going to report several questions which brought about in producing the J.E. virus vaccine by alcohol precipitation, protamine sulfate treatment method. The results obtained were as folows ; 1) In process treated with 40% alcohol, we used to ethanol made in Germany, but it was too expensive to use it. As the result which we had studied about it, we were satisfied with J.E. virus vaccine which produced with alcohol made in Korea, and then, we treated with accurate specific gravity of 40% ethanol for the precipitation of the virus. And also, we knew that it was the best method to be treated it for 3hrs, $13^{circ}C$. 2) When we treated with protamine sulfate (0.025mg/ml), we acquired the highest potent titer, and suited into purpose for the nitrogen concentration. 3) The filtration of the purified J.E. virus vaccine, in case of millipore filter paper of large pore size was not suitable for the sterility. Therefore the pore size less than 0.8.$mu$ (AA filter paper) in millipore filter paper was very suitable. But it seemed to be important subhects that the smaller was the pore size, the lower was the potent titer.