Abstract: Objective To explore the effects of benzo(a)pyrene(BaP)exposure on spatial learning and memory abilities and ultramicro structure of hippo campal neurons in rats.Methods Fifty healthy male SD rats were randomly divided into a control group,a solvent control group and three BaP-treated groups.The exposure groups were treated by intraper itoneal injection with 2.5,5,and 10 mg/kg BaP once a day,respectively.The rats in solvent control group received anequal volume of cornoil.The treatment was lasted for 30 days.The capability of learning and memory of the rats were mea sured by Morris water mazetest.The specmiens of hippocam pus were sliced and the morphological changes were observed with transmission electron microscopy.Results The times of passing through the platform were 12.03±2.43,11.35±2.68,9.75±1.78,7.63±1.67,and 4.38±1.46 and the time(in second)of staying around the platform were 46.34±11.56,48.12±13.22,32.35±7.68,26.13±5.34,and 16.14±3.15,respectively,for the rats of blank control,solvent control,low-,moderate,and high-dose BaP treamtent group.A significant mipairment in Morriswater maze performance among the BaP-treated rats was observed compared with the controls(P<0.05).There sults also showed that damages of ultramicro structure of hippo campal neurons were significant in the BaP-treated groups compared with that of the controls.Conclusion BaP has neuro behavioral to xicity in rats.