Chronological changes of bisphenol A (BPA) concentration were investigated for a week in mature medaka (Oryzias latipes) and spawned eggs (embryo) after exposing the fish to BPA at a concentration of 100 µg/l in water. The BPA concentrations in mature fish and spawned eggs increased beginning at the day after initial exposure, and reached an approximately constant level on the second day. On the other hand, the decrease in BPA concentration in the parent body was rapid after being placed back into pure water (average decrease was 87% on the first day, and 98% on the second day), while approximately 24% of the BPA in the spawned eggs from the parents remained after the fourth day in pure water. Thus, it was assumed that there is no system for BPA excretion from eggs. Another experiment was conducted, in which eggs spawned from a parent on the fourth day of exposure were raised in pure water. The BPA concentration in the eggs on the sixth day was approximately 29% lower when compared to that at spawning. Therefore, it was assumed that the embryo cannot conjugate BPA incorporated into the egg due to an underdeveloped metabolic or excretion mechanism.