It has been recently reported that the consumption of a high-fat diet during pregnancy exerts various effects on fetuses and newborn mice. The purpose of this study was to determine the effects of a high-fat diet during pregnancy on the expression of cytochrome P450 (CYP) in the livers of offspring. Mouse dams were fed a high-fat diet during pregnancy from the time of conception. After their birth, the newborn mice were fed a normal diet until 12 weeks of age. In the livers of the infant male mice that consumed a high-fat diet, the protein expression of CYP3A and CYP2C was decreased, and the protein expression of CYP1A and CYP2E was increased at 6 and 12 weeks of age. However, almost no changes were observed in the CYP proteins at 6 and 12 weeks of age in the livers of the infant female mice that consumed a high-fat diet. The amount of pregnane X receptor (PXR) translocated into the nucleus was reduced in the livers of infant male mice that consumed a high-fat diet. However, there was neither an increase in tumor necrosis factor-α or interleukin-1β nor a decrease in lithocholic acid. These data suggested that CYP3A and CYP2C might decrease as a result of the decrease in the amount of nuclear PXR in infant male mice that consumed a high-fat diet. The results of this study suggested that the consumption of a high-fat diet by pregnant mothers may be one explanation for individual differences in pharmacokinetics.