Objectives: To investigate histopathological changes in the lungs and morphological changes of newborn rats whose mothers are exposed to methidathion (MD) during their pregnancy, and also the effects of caffeic acid phenethyl ester (CAPE) on these changes. Methods: The study was conducted in the Faculty of Medicine, Suleyman Demirel University, Isparta, Turkey between May and June 2007. Fifty female Wistar albino rats were randomly divided into 5 groups, as follows: Group I (n=10): control group, Group II (n=10): 5mg/kg/day MD treated group in the first 7 days of pregnancy, Group III (n=10): 5 mg/kg/day MD + 10 mu mol/kg/day CAPE treated group in the first 7 days of pregnancy, Group IV (n=10): 5mg/kg/day MD treated group in the last 7 days of pregnancy, and Group V (n=10): 5 mg/kg/day MD + 10 mu mol/kg/day CAPE treated group in the last 7 days of pregnancy. The MD was administrated by oral gavage in corn oil, and the CAPE was administrated intraperitoneally. Results: Tremors, agitation, and spasm of extremities were observed in pregnant rats after administration of MD. Histopathological examination of lung tissues revealed peribronchial inflammation, alveolar and bronchoalveolar hemorrhage, intraparenchymal vascular congestion and thrombosis, alveolar destruction, and intraparenchymal infiltration. Conclusions: Methidathion causes low weight gain and deaths among pregnant rats, increases intrauterine fetus deaths, causes low birth weights in the newborns, and histopathological changes in the lung tissues of newborn rats. The CAPE has an ameliorating effect on these histopathological alterations.