A Philometra sp. (Nematoda: Philometridae) was first found on the testis and the ovary of the red sea bream, Chrysophrys major, cultured at a farm on the coast of the Amami Island, Kagoshima prefecture. In male fish small masses of several immature female worms were found under the the serous membrane of various parts of the testes, but a large mass of the mature worms was observed only in the connective area of the testes. These observations suggest the worm can develope only in this area. All the large masses of worms were covered with a thin clear membrane originated from the testis serosa. In female fish mature worms were found to be free in the parenchyma of the ovary. The whole body of the worm could not be collected perfectly, because the body wall was very thin and weak against handling and always several worms were entangled complicatedly with each other. Observation was made on the head parts of three fixed specimens. The results were as follows : body length unmeasured; maximum width 0.50-0.57 mm near uterus end and 0.98-1.06 mm behind intestine end; cuticle smooth, 3μ thick; head broadly rounded, without papillae; pharynx 0.98-1.10 mm in long, with bulbus anterior swelling of 0.10-0.12 mm in diameter; anterior ovary partially unobservable; uterus locates 0.33-0.44 mm behind head end, with spherical eggs of 16-18 μ in diameter. The present species differed from P. spari YAMAGUTI, 1961 in not only the habitat of the worm in the host but also the location of the uterus in the gravid female worm. The latter was collected from the swim bladder of the gilthead, Mylio macrocephalus, and its uterus was reported to arise behind the anterior end of the intestine.