In recent years, the free radical theory of aging has attained great interest. Many studies on aging using tissue homogenates and subcellular fractions have provided evidence for the occurrence of lipid peroxidation. However, there are studies which report decrease or no significant change in parameters of lipid peroxidation. In our study, we investigated whether hepatic lipid peroxidation levels in male Swiss-Albino mice change with age. Three groups of animals, 3, 6 and 18 months old, were used. The diene conjugate and malondialdehyde levels of liver homogenates, mitochondria and microsomes were measured. Significant increases in both diene conjugate and malondialdehyde levels of liver homogenates and mitochondria have been observed in 18-month-old mice when compared with those aged 3 and 6 months. As for microsomes, only malondialdehyde levels were elevated in the old group when compared with young and adult groups. Both parameters were significantly increased in aged mice which indicate that lipid peroxidation is important in advancing age in mice.