Abstract: Objective To observe the change of the ability of learning and memory in the rats infected with Toxoplasma gondii(T.gondii)and to examine the contents of superoxide dismutase(SOD),malodialdehyde(MDA),and nitric oxide (NO)in peripheral blood and brain tissue of the rats. Methods Totally 48 male Wistar rats were randomly devided into a group with T.gondii infection and a control group without the infection.Suspension of T.gondii(2×10⁷/ml,2ml)was injected intra-peritoneally into the rats in the experimental group.Then Morris water maze test was performed to observe the behavior changes of the rats at 1,2,4,8 week after the injecttion.The levels of SOD,MDA,and NO in the peripheral blood and brain tissue were tested. Results The average time and the average distance for the rats in test group was 31.1±1.6 s and 1 066±3.2 cm,and those of the control group were 19.6±2.8 s and 772.0±6.9 cm,with significant differences between the tow groups(P<0.05).The levels of SOD in peripheral blood and brain tissue were 91.2±8.3 U/mL and 78.9 ±3.2 U/mL for the rats of the test group and those of the control groups were 138.6±10.4 U/mL and 111.6±5.3 U/mL and those of the test group markedly decreased than the control group(P<0.05).The levels of MDA in peripheral blood and brain tissue of the test group were 22.1±1.3 nmol/mL and 7.8±2.0 nmol/mL,and those of the control group were 14.5±1.9 nmol/mL and 5.0±1.2 nmol/mL.The level of NO in peripheral blood and brain tissue of the test group were 21.5±3.1μmol/mL and 29.9±1.8μmol/mL,and those of the control group were 14.0±2.6μmol/mL,19.1±2.2 μmol/mL.Compared with the control group,the concentration of MDA and NO in the test group increased markedly (P<0.05). Conclusion Infection with T.gondii can induce harmful effects on the ability of learning and memory in rats obviously.In addition,T.gondii can induce the decrease of SOD and the increase of MDA and NO,which may be one of the mechanism of T.gondii-induced behavior change in rats.