Preclinical data of fetal, infant, and juvenile animals are important for the prediction of drug toxicity in fetuses and children. However, expression of drug-metabolizing enzymes, including cytochromes P450 (CYPs), have not been fully investigated in fetal, infant, or juvenile liver of the cynomolgus macaque, an animal species important for preclinical studies. In this study, hepatic expression of 20 cynomolgus macaque CYPs (mfCYPs) in the CYP1-4 subfamilies that are relevant to drug metabolism was measured in fetuses, infants, and juveniles using DNA microarrays. Expression of most mfCYPs, including those moderately or abundantly expressed in postnatal livers such as mfCYP2A23, mfCYP2A24, mfCYP2B6, mfCYP2C9, mfCYP2C19, mfCYP2C76, mfCYP2D17, mfCYP2E1 mfCYP3A4, and mfCYP3A5, was much less abundant in fetal livers, but increased substantially after birth. In contrast, expression of mfCYP2C8 in fetal livers was not substantially different from postnatal livers. Since human CYP3A7 is expressed more abundantly in fetal livers than in adult livers, mfCYP3A7, an ortholog of human CYP3A7, was analyzed by quantitative polymerase chain reaction. Expression of mfCYP3A7 in fetal livers was much lower than that in postnatal livers, and greatly increased after birth, unlike the expression of human CYP3A7. These results indicate that expression of most mfCYPs examined was low in fetal livers, but increased greatly in postnatal livers, with a few exceptions such as mfCYP2C8.