Low density culture, (0.24-0.26 ind./m2) of barfin flounder, in large sized aquaria was undertaken to establish a culture system for stable procurement of the fertilized eggs. Captured females spawned repeatedly for approximately one month, and the total number of spawned eggs during a spawning season was averaged between 85,000 to 406,000 per one female. Both fertilizing rate and hatching rate were high, 84-87% and 39-66%, respectively, and almost same as those from artificial fertilization using eggs within one day after ovulation. These results thus demonstrated the usefulness of this low density culture for stable harvest of a number of fertilized eggs with good quality. The spawning of the barfin flounders was estimated to occur from 10 p.m. to 4 a.m. in the aquaria based on the serial observation of embryonic development in artificially fertilized eggs.