Parasitological examinations were made on the tissues and the blood of the black bears (Selenarctos thibetanus japonicus) of Japan. Three kinds of filarial parasites were found in the tissues and the blood of the hosts: Dirofilaria ursi, Tetrapetalonema (Tetrapetalonema) akitensis sp. n. and Dipetalonema (Chenofilaria) japonica sp. n. The male and the microfilaria of D. ursi were described from the type host animal. Japanese specimens of D. ursi were compared with the specimens from American black bears of Alaska and Canada, and it was found that the measurement data obtained were similar to each other. Within the subgenus Tetrapetalonema, T. akitensis resembled T. interstitium and T. llewellyni of North America, but was distinguished from them by the longer esophagus and smaller microfilariae. Several other species of the same subgenus from monkeys of South America were different from T. akitensis due to the presence of the terminal nucleus of their microfilariae. Wihtin the subgenus Chenofilaria, D. japonica closely resembled D. johnstoni and D. pearsoni of Australia, but was different from D. johnstoni due to the salient preesophageal cuticular ring and relatively longer tai of the female. Besides, D. pearsoni was much longer than D. japonica in the body length.