Using the hepatitis virus isolated from hepatitis patient. the author purified the virus by HASHIMOTO'S method, and studied some properties that were supposed to be important for the virus; the resistance to disinfectant and ether, the inactivation by ultraviolet rays and the filtrability. The following results were obtained. 1) For the study of the properties of the virus the author adopted the pathological findings as to determine the causable change by the infection. This method was assumed to be reasonable in spite of the dispute for the good agreement of both results obtained by tests on the purified and unpurified virus. 2) The virus was resistant fairly good for disinfectant, hence it needed for over 3 weeks to inactivate the virus completely by the action of disinfectant, and the virus gradually lost its activity as the duration of disinfectant treament. 3) It was confirmed that the virus was filtrable well through the Seitz EK filter and resistant to the action of ether. Also the virus could stand against the irradiation of ultraviolet rays for less than 40 min. 4) By the intraperitoneal injection of inactivated virus for 3 times, the animal could be immunized for the challenge of the same or the other type virus. But in sometime slight pathological changes were observed, and this implied the immunization thus obtained was not so stiff as capable for immunising the all challenge.