In the present report the author studied the biological natures of the isolated virus, particularlv on the influence of physical and chemical factors on it. The virus, which was isolated from the infectious hepatitis patients and was preserved by the passage through embryonated hen's eggs or mice, was used throughout this work. The results were as follows: 1) The influence of the rain-water, well-water and sea-water, which were taken from the hepatitis-prevailing areas, on the isolated virus were studied. The virus survived for a long time in rain-water, and could survive for a longer time at lower temperature than at 18° to 30°C. From the results of infection test on mice, it was presumed that the virus could be preserved for 6 to 7 weeks under the usual conditions. 2) By the investigation of the influence of other physical and chemical factors on the virus, it was confirmed that this virus had the natures simillar to those described by the senior investigators, e. g. filtrability through Seitz E. K. etc. These biological natures, together with the heat and disinfectant-resisting natures, were conceived to be the important characters being useful for the identification of hepatitis virus.