Plasticizers are chemical additives that enhance plastic flexibility. They are ubiquitous environmental contaminants and are commonly found in river and lake waters (Fromme et al 2002). The present study aimed to investigate the effects of a water-soluble plasticizer, dibutyl phthalate (DBP) on developing Medaka ("Oryzias latipes") embryos. Three concentrations of DBP (5 microgram/L, 25 microgram/L, and 45 microgram/L) were used to treat groups of 10 eggs, and death, developmental stages, and any morphological abnormalities were observed for 5 consecutive days. Embryos with asymmetrical eyes and missing eyes were observed in the DBP groups. In addition, dose-dependent mortality and developmental delays were also observed. 45 microgram/L and 25 microgram/L were lethal by the 5th day. The results indicate that DBP poses an environmental hazard to developing fish. (Contains 6 figures.)