I have succeeded to isolate the Rickettsia like bodies in the protoplasma of Epiteloidcells and Monocytes in the peritoneal fluid of the mouse which had been challenged by five strains. 1) Five strains isolated from rats did not indicate something colonies. 2) Concerning with rabbits. I have recognized the testicular swelling sometimes by intratesticular injection by the 5 strains isolated. I have tried W. F. R. two or more times. and have found that, Agglutinin tieters against OXK has increased from 1. 80 to about 1 360. 3) Concerning with the Guinea pigs, 5 strains did not occur Neil-mooser reaction by intraperitoneal injection. 4) On the mouse, I have recognized Rickettsia like bodies in the protoplasma of Epitheloidcells and Monocytes when the 5 strains isolated had been injected intraperitonealy. 5) On the rats, 5 strains isolated did not occur Maxcy's phenomenon by its intraperitoneal injection, but has occured consolidation of lung and Rickettsia like bodies were recognized by Giema stains. So I have determined the 5 strains isolated from rats as Rickettsia orientalis groupe. I have known that, these Rickettsia strains can be isolated at summer, and do not at winter, spring or autumn from Rattus norvegicus only.