Peroxisome proliferator-activated receptors (PPARs), members of the nuclear hormone receptor superfamily of transcription factors, are key regulators in various pathophysiological processes related to energy metabolism including lipid, carbohydrate metabolism, and inflammation. At present, little information is on the effect of age and calorie restriction (CR) on PPARs. In the present study, we investigated how age and CR (60% of the ad libitum intake) modulate PPARs in kidneys obtained from Fischer 344 rats, ages 13 and 25 months. Results showed that nuclear protein, mRNA level, and DNA binding activity of PPARs decreased with age, while CR blunted the reduction. Our findings were verified in separate experiments in which rats were injected with lipopolysaccharide, with the result of increased susceptibility to inflammation. Based on these findings, we conclude that the altered expression of PPARs may be due to increased oxidative stress with age, and that CR prevents these decreases through its antioxidative action.