Neopercis sex fasciata (Temminck et Schlegel) is a Trachinoid fish, inhibiting sandy bottom of the coasts of southern Japan. It attains some 200 mm in total length when full grown. The spawning season seems to extend from early March to early June in Kyushu (Table 1). The author operated artificial insemination of this fish on March 9, 1954, on the coast of Miyazaki Prefecture, and observed the egg development and hatched larvae (Plate 16, figs. 1-11). The egg is bouyant, colorless and spherical in shape, measuring 0.77-0.93 mm in diameter, with a single colorless oil-globule measuring 0.16-0.23 mm in diameter (Table 1). The hatching took place about 3 days after insemination (70-75 hr.) at the water temperature 12-17℃. The larva just hatched is 2.15-2.30 mm in total length with the oil-globule situated in the posterior part of the yolk, partly protruding from the yolk surface. The myotome number is 9+25=34 (vertebral number of this fish is 10+22=32) (Fig. 8). In four days after hatching the yolk was entirely consumed (Fig. 11). The anus is situated far forward, under 5th myotome, suggesting the backward shifting of anus during larval development.