In January 2009, the water quality of offshore around the Incheon coast was evaluated by bioassay using early development systems of a sea urchin species, Hemicentrotus pulcherrimus. The results of performing biological evaluations on seawater samples from total of thirteen sites, showed that the formation rates of normal pluteus larva varied from 18% to 71%. In site 5 the seawater sample led to an averaage formation rate of normal larva of 18%, the highest abnormal formation rate hindering the early embryo development of the experimental animal, while that of site 3 averaged 71%, the highest formation rate of normal larva. Seawater samples from site 1, 2, 4, 7, 9, 10, 11 and 12, resulted in average formation rates of normal larva from 33% to 56%, which indicates the developmental damage of early embryos is not severe. Seawater samples from site 5, 6, 8 and 13, resulted in average formation rates of normal larva from 18% to 21% which there was strong damage to the development of early embryos.