It has been already shown that the tsutsugamushi disease rickettsia obtained from the infected mouse of this disease, that mouse was repeatedly injected small dose of chloramphenicol, is highly capable of inducing the disease to the chlorpromazine treated guinea pig leading to the much production of ascites and the antigenic capacity of this ascites was inferior to that obtained from the infected animal by the original strain of the organism owing to the variation on some properties of the organism by chloramphenicol. The author studied the complement fixation reaction using the original strains, OSEKI's, MITANI's, and HICHITO strains and the strains obtained by variation of these and found some specificity on the antigen. In any case of the test, the ascites was obtained from the organism inoculated guinea pig and used as antigen for complement fixation reaction. From the view of the results, all ascites obtained by inoculation of the original strains showed difinite strain specificity to the corresponding antiserum, but those by the varied strains showed only slight inhibition on hemolysis in any case just like having no strain specificity. Hence, it was confirmed that the occurence of variation on the properties of the tsutsugamushi disease rickettsia by action of chloramphenicol.