An experiment was conducted to explore the anti-aging effect of oleuropein on aging mice induced by D-galactose and relevant mechanisms. Forty mice were randomly divided into normal control group, aging model group, oleuropein treated group, and vitamin E control group. Aging mice models were developed using D-galactose. The viscera index was determined. Spectrophotometry was used to detect the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and the content of malondialdehyde (MDA) in the heart, liver and brain of the mice. PCR-ELISA was used to measured telomerase activity in the heart, liver and brain. The levels of serum IgG, IgM and complement C3, C4 and interleukin-2 (IL-2) were detected by ELISA and radioimmunoassay, respectively. The results showed that oleuropein could significantly increase the viscera index, elevate the activities of SOD and GSH-Px, decrease the content of MDA, and increase telomerase activity in the heart, liver and brain of the mice and the levels of serum IgG, IgM and complement C3, C4 and IL-2 (P<0.05, P <0.01). The above aging related biochemical indexes returned the level close to the normal after oleuropein treatment, and no statistical difference was found in the treatment efficacy compared with those in vitamin E control group (P >0.05). The study suggested that oleuropein could delay aging, which may be related to antagonizing free radical injury and enhancing the telomerase activity in the heart, liver and brain, and immune function of D-galactoce- induced aging mice.