Effects on nonylphenol (NP) treatment on early development of fertilized eggs and survival of larvae in olive flounder, Paralichthys olivaceus were investigated. Fertilized eggs and hatched larvae were exposed to aqueous solutions of NP at nominal concentrations of 50, 100, 150 and 200μg/L. In the control I and Ⅱ(methanol-carrier control) groups, the hatchability of fertilized eggs were 90.7±7.02 and 90.0±5.29%(P<0.05), respectively. However, treatments of NP concentrations at 50, 100, 150 and 200μg/L were reduced to 78.7±4.16, 46.0±9.l7, 48.0±3.46 and 33.31±11.02%(P<0.05), respectively. The time to hatching of fertilized eggs was delayed in high-dose NP treatment groups rather than control groups. Fertilized eggs of NP immersed group could not hatch normally, and also vertebra of the larvae observed as abnormal shape. Cumulative mortality of hatched larvae after 26hr NP treatment was 38.3, 78.3, 88.3 and 100% in NP 50, 100, 150 and 200μg/L treatment groups, respectively. Whereas, control I and Ⅱ were 11.7, 16.7%(P<0.05). Hatched larvae showed most death at the embryonic development stage with abnormalities. These results suggest that NP treatment in fertilized eggs and larvae was inhibited as normally development for fertilized egg and growing of larvae.