The present study was performed to investigate the potential toxic effects of prenatal exposure to 4-tert-octylphenol (OP) on liver, kidney, spleen, and hematologic parameters of male and female rats in adult life. The rats were treated with OP subcutaneously in utero at doses of control (vehicle, corn oil), 100 or 250 mg/kg per day. After birth, the rats were allowed to grow until adulthood and then liver, kidney and spleen were investigated histopathologically. Also the blood collected from rats were analyzed for any hematologic changes. The red blood cells of male and female rats were decreased in 250 mg/kg per day OP-treated group compared with the control group. mu-RBC of male rats in high dose treatment groups were increased significantly compared with the controls and 100 mg/kg per day treatment groups. mu-RBC of female rats in treatment groups were increased in a dose-dependent manner compared with the controls. In liver, kidney and spleen of male and female rats treated with OP, degeneration of hepatic parenchyma, tubular degeneration and hemorrhage were observed in histopathologic examination. The hemosiderin deposition in spleen of the high-dose group was increased in both male and female rats. In conclusion, findings of this study demonstrate that maternal administration of high doses of OP causes adverse effects on spleen and liver tissues of male and female offsprings at adulthood. Specifically, OP caused decreases in the number of red blood cells indicated by increased destruction in the spleen.