Objective: To determine the effects of chaihu on learning and memory of mice. Methods: The mice were injected intra-peritoneally with different doses of chaihu twice per day for five days, then learning and memory behavior was examined using Y-maze, and the activity of superoxide dismutase（SOD）, the levels of malondialdehyde（MDA） and nitric oxide（NO） were measured by spectrophotometry. Results:The administration of chaihu improved learning and memory in a dose dependent manner, and was most effective at a dose of 400 mg／kg body weight. The memory consolidation was enhanced significantly from 24 to 72 h after training, especially 24 h after training. SOD activity and NO level were increased significantly（P < 0.01）, but MDA level was reduced in brain tissues. Conclusion: The administration of chaihu could improve the capability of learning and memory which might be associated with enhancing the antioxidant action and the alteration of NO level in brain tissues.