MURAKAMI and his collaborator had isolated the hepatitis virus from hepatitis patient and cultured in the chorio-allantoic cavity of chick embryo. The author newly isolated the hepatitis virus from the patient and studied on virological properties of the virus having obtained the purified virus. The following results were obtained. 1) In the treatment by heating or by disinfectant, the purified virus showed high resistance to these treatment, and these resistances were thought to be the featuring properties of the virus. 2) Also it was observed that the virus was highly resistant to irradiation of ultraviolet rays, and to action of ether. 3) The purified virus was highly infections to mouse by peroral administration of it. The pathological changes were observed conspicuously, and moreover the changes induced were just the identical in any case. 4) By the serological study, it was observed that the purified virus had an eminent antigenic capacity and reacted with the immune serum obtained by inoculation of the virus to rabbit giving the antigenic titier of 1:64-1:128. Also the virus showed distinctive reaction in the complement fixation test using the convalescent patient's serum from hepatitis; hence, this test might be highly valuable for the serological diagnosis of hepatitis despite of rather low titer than the above. 5) The most difficult problem was the identification of neutralizing effect in the neutralization test and “Absättigungsversuch”. For this purpose the author adopted the mitigation of pathological changes caused by the neutralizing effect and observed the marked mitigation of the changes on the test using the virus and corrsponding immune serum; but this evidence was not observed in the test of the virus and uncorresponding serum. The mitigation of the changes was not distinct in the "Absättigungsversuch" possibly by the occurence of combination of the virus and its anti-body in the body of animal instead of in the test tube. It is to be expected the further study on the test procedure and the method of identifying the neutralization effect.