Objective To research effects of chronic exposure to benzo[a]pyrene（BaP）on learning and memory ability of SD rats.Methods 60 SD rats were randomly divided into solvent control group and BaP exposure group（low-dose group

medium-dose group and high-dose group）.In the solvent control group

vegetable oil was injected into the rats′abdominal cavity

and different doses of BaP were injected into rats′abdominal cavity in the BaP exposure group for 10 weeks.After the BaP exposure

the Morris maze experiment was used to evaluate learning and memory ability of rats.Results In the process of study all the rats exposed to BaP showed some abnormal behaviors.In the navigation experiment

as the days of experiment increased escaping and hiding time of rats from each group decreased.And within a day the average escape latent period of rats in each group was different with statistical significanre（P<0.01）.The average escape latent period of solvent control group was obviously shorter than the BaP exposure group

and during 4days after the experiment started as the dose of BaP exposure increased

the average escape latent period of rats increased correspondingly

and there was statistical significance（P<0.05）.In the space exploration experiment

when compared the time needed to find the original platform the first time

the number of times crossed the original platform and lengthy of stay on the original platform for rats in each group

the differences was statistical significant（P<0.01）

among which the rats in solvent control group used less time to first find the original platform and crossed the original platform more often than BaP exposure group and also stayed longer on the original platform

and as the dose B[a]P increased

the rats used more time getting back to the original platform first

crossed the original platform less times and stayed shoter on the platform quadrart.and there was statistical significance（P<0.05）.Conclusion Chronic exposure to BaP could harm the learning and memory ability of rats and the learning and memory ability decreased as the dose of BaP exposure increased

which showed that there is a dose-effect relationship related with the effect of BaP exposure on rats′learning and memory ability.