Mice were inoculated with living and inactivated vaccines of Rickettsia tsutsugamushi by various different routs, intraperitoneal, intracutaneous, subcutaneous, intracerebral and intratracheal. The grade of immunity of thus treated mice was studied in respect to the sorts of vaccines and the routs of inoculation. Mitani and Tanizawa strains of Rickettsia tsutsugamushi were used as the test agents. The results were as follows: 1) Irrespective of the routes of inoculation and life or death of vaccines, the production of antiboies in mice remained almost independent of the sorts of rickettsial strains. 2) In the case of inoculation of living vaccines, the production of antibodies was the best in those inoculated by intracutaneous route and decreased in the sequence as follows; subcutaneous, intraperitoneal, intracerebral and intratracheal. 3) In the case of inoculation of inactivated vaccines, the inoculation by intraperitoneal route produced the antibodies in the largest amount, and the antibody production decreased in the following order; intracutaneous, subcutaneous, intracerebral and intratracheal. Namely, the production of antibodies in mice largely depends on the nature of vaccines as well as the inoculation routes. Regardless of the nature of vaccines, however, intraperitoneal inoculation seems to produce the highest immunity.