In order to study hybrid offspring's embryonic development, postembryonic development and growth characteristics under different temperatures, crossing test was carried out using frozen sperms of summer flounder(Paralichthys dentatus) and eggs of Japanese flounder(Paralichthys olivaceus). The development of the hybrid embryos was successively observed and described under Olympus microscope. After 65 hours and 57 minutes the embryonic development finished, which contains cleavage stage, blastula stage, gastrula stage, closure stage of blastopore, somites stage, tail bud stage, heartbeating stage, and hatching stage. Then the embryos began postembryonic development. During the embryonic development the heart began to beat at 15 minutes after the embryos moved. Morphological characters and growth of the fries were also observed by Olympus dissecting microscope and recorded once every day. According to these, the postembryonic development was divided into four stages: yolksac absorption stage (1-6 days after hatching), premetamorphosis stage (7-25 days after hatching), metamorphosis stage (25-30 days after hatching) and growth stage after metamorphosis. The embryonic development at 16-17 ℃，18-19 ℃，20 ℃ and 22-23 ℃ was studied. Result showed that the hybrid embryos developed better at 16-20 ℃, and a great deal of the fries hatched at 22-23 ℃ died 2-3 days after hatching. Growth of the postlarva at 18-19 ℃, 20 ℃, 22 ℃ and 24 ℃ was also studied, result showed that the metamorphosis and the growth rate of metamorphosis stage postlarva were higher at 22-24 ℃ than that at 18-20 ℃.