Artemisia annua L. (AA) is a traditional Chinese medical plant. Also, It is well-known to contain a significant level of artemisinin which is an anti-malarial agent and is also reported to have antitumor activity at high concentration. Our previous study showed that the ethanolic extract of Artemisia annua. L had in vitro antioxidant effect and induced antioxidant enzyme NQO1 activity in murine hepatoma Hepa1c1c7 and BpRc1 cell line. In the present study, we investigated whether or not AA attenuates oxidative stress and DNA damage induced by D-galactose in mouse model. Our results indicated that D-galactose treatment for 6 weeks caused cognitive impairment in Morris water maze test and produced oxidative stress as is evidenced by the increase of lipid peroxidation and 8-OH dG level in plasma. Furthermore, we found that D-galactose treatment caused several histological change in some tissues. The treatment for 6 weeks with AA extract attenuated cognitive impairment, lipid peroxidation and DNA damage, and induced some antioxidant enzymes (HO-1, NQO-1, GR, GPx) in mice injected i.p. with D-galactose. In addition, AA extract could prevented histological damage of some tissues caused by D-galactose. In conclusion, AA extract suppressed memory impairment induced by D-galactose in mice, maybe through inhibition of ROS generation in brain tissue by D-galactose.