Since the Japanese pond frogs (Rang nigromaculata and R. brevipoda) are known to be very closely allied with each other in morphological, ecological, physiological or immunological characters, the phylogenetical relationships between the Japanese pond frogs and other 10 species of Japanese amphibians were investigated by means of immunoelectrophoretic analysis of liver extract. The results obtained are as follows: (1) There are conservative antigens which are commonly found in all species of Anura. (2) The Japanese pond frogs have specific antigens. (3) R. nigromaculata and R. brevipoda are very closely allied with each other. (4) Four species of the genus Rana (R. rugosa, R. catesbeiana, R, ornativentris and R. japonica) are closely related to the Japanese pond frogs. (5) Two species of the genus Rhacophorus (Rh. arboreus and Rh. buergeri) are related to the Japanese pond frogs. (6) R. limnocharis is related to the Japanese pond frogs at the same extent as the genus Rhcophorus is. (7) Two species of the suborder Procoela (Hyla arbored and Bufo bufo) are only partially related to the Japanese pond frogs. (8) Cynops pyrrhogaster pyrrhogaster of Urodera had only a few common antigens with the Japanese pond frogs.