Japanese flounder ( Paralichthys olivaceus) , which naturally inhabits the seas of China , Korea , Russia andJapan,hasbecomeoneofthemostimportantcultivatedspecies. Inordertodocryopreservationresearchof the Japanese flounder embryos , it is important to define definitely embryo developmental stage. In addition , study of Japanese flounder embryo development will provide support for the fry breeding. In the present study , embryonic development of Japanese flounder cultured in hatchery was studied. Japanese flounder embryos were incubated in sea water (salinity : 29. 9) at 14 -16 ℃ and the course of embryonic development was observed consecutively under Olympus microscope. The total development time of every development stage was noted and calculated and the characteristic images were taken using Olympus camera. The characteristics and time of 29 embryonic development stages were noted from the fertilization to the hatching after 5 d. 30 photographs , representing the characters of all the development stages and fry , were taken. The time2table of major embryonic development stages of Japanese flounder was as follows : blastodisc forming stage at 0. 5 h post fertilization (pf) ; four cell stage at 2. 5 h pf ; morula at 10. 5 h pf ; low blastula stage at 17 h pf ; early gastrula stage at 20 h 10 m pf ; late gastrula at 28. 5 h pf ; blastopore closing stage at 29 h 44 m pf ; nurula stage at 30 h 40 m pf ; 4 -5 somite stage at 35 h 20 m pf ; 15 -20 somite stage at 40 h 10 m pf ; tail bud stage at 49 h 10 m pf ; heart beating stage at 67 h 12 m pf; embryo movement at 75 h 10 m pf; pre2hatching stage at 90 h 9 m pf ; hatching stage at 93 h pf. Yolk sac was completely absorbed 190 h after fertilization and then entered metamorphosis stage.