AbstractThis experiment studied the effect of Cordyceps sinensis extract (CSE) on mice aged by d‐galactose and castrated rats to analyse its antiaging effect. Water maze and step‐down type avoidance tests were used to examine the effect of CSE on learning and memory. CSE shortened escape latency, prolonged step‐down latency and decreased the number of errors in mice aged by d‐galactose. The effect of CSE on the sexual function of castrated rats was evaluated by measuring the penis erection latency, mount latency and ejaculation latency. CSE appeared to shorten penis erection latency and mount latency in castrated rats. The study also measured the effect of CSE on the activity of age‐related enzymes. The results showed that CSE improved the activity of superoxide dismutase, glutathione peroxidase and catalase and lowered the level of lipid peroxidation and monoamine oxidase activity in the aged mice. The study demonstrated that CSE can improve the brain function and antioxidative enzyme activity in mice with d‐galactose‐induced senescence and promote sexual function in castrated rats. All of these findings suggest that CSE has an antiaging effect. Copyright © 2008 John Wiley & Sons, Ltd.