Carboplatin, an oncostatic drug, was administered intravenously to pregnant Crj : CD (Sprague-Dawley) rats from day 17 of gestation through day 21 of pospartum at dose levels of 1, 2 and 4 mg/kg/day. The summerized results obtained are as follows : 1. Maternal body weight gains were suppressed during the former part of the lactation period at carboplatin 2 mg/kg and higher. 2. Thymic weights were decreased and lung weights were increased in dams (F₀) at carboplatin 2 mg/kg and higher. Further, ovarian weights were reduced in dams (F₀) at carboplatin 4 mg/kg. 3. Carboplatin failed to affect the parturition of F₀ dams. 4. Carboplatin did not affect the viability of newborns (F₁), and postnatal differentiations, early behavioral developments, learning ability, mortor activity or emotional development in F₁ animals. 5. Carboplatin 4 mg/kg brought a suppression of pituitary weights after mating in F₁ male rats and decreases of adrenal and genital organ weights at weaning in F₁ female rats, but failed to affect their reproductive ability. 6. Influences on prenatal development were not apparently observed for F₂ fetuses derived from F₁ rats whose dams had ever recieved carboplatin during the perinatal and lactation periods. Based on these results, the no-effect dose level of carboplatin under the present experimental condition was estimated to be 1 mg/kg/day against dams and 2mg/kg/day against their offspring.