Induced rate,growth and gonad were studied in triploid Japanese flounder(Paralichthys olivaceus).The result indicated that triploidy flounder was achieved successfully by cold shocking fertilized eggs at 3 ℃ for 45 minutes duration,3 minutes after fertilization when the temperature of fertilization was 14.8-15.5 ℃.Regular growth measurements were done on the achieved triploid Japanese flounder and the control group 120 days,348 days and 630 days after that.The results revealed that there was no significant difference in growth between diploid flounder and triploid flounder after 120 days.But the weight was significantly different between them after 348 days(P<0.05).And the triploid growth rates(full-length,weight)showed extremely significant difference compared to the diploid controls’(P<0.01).The indexes of the ovaries and the testes in the diploid control were respectively 3.3 and 3.1 times of the indexes of the ovaries and the testes in the triploid Japanese flounder.Furthermore,the gonadosomatic indexes(GSI)of the triploid were significantly higher than the control group’s after 630 days(P<0.001).From these gonadal sections,a lot of normal oocytes could be found in the section of diploid ovary,but the triploid ovary stayed in the stage of oogonium stage.Meanwhile,the number of spermatocyte in triploid testis was significantly less than that of the number of spermatocyte in diploid testis.The study obtained 100% triploid rate with this method.Meanwhile,the triploid gonad was hypogenetic and the growth rate of the triploidy was significantly higher than the control group.Thus,the triploid is suitable for promotion in production.