Objective To investigate the relationship between neural cell cytotoxicity, apoptosis and cytochrome P4501A1(CYP1A1) mRNA exposed to benzo (a) pyrene ［B(a)P］. Methods Primary neural cells were dissociated from the cerebral cortex of 1-3 days old SD rats and cultured in a DMEM incubator at 37℃. After cultivation for 5 days, the well-grown neural cells were selected and treated with the concentrations 0, 10, 20 and 40μmol/L of B(a) P respectively. The neural cells were further cultivated for 40 hours. Neural cell vitality was detected using cck8 kit. Apoptosis rate was measured by flow cytometry using annexinV -FITC and propidium iodide (PI) staining. CYP1A1 mRNA was tested with RT-PCR technique. CYP1A1 mRNA protein expression was determined by immunohistochemistry SABC. Results With the increase of B(a) P concentration, the neural cell vitality declined in both the medium dose group and the high dose group compared with controls, and early apoptotic rate increased steadily only in the high dose group compared with controls. Trend test indicated that cell vitality declined and apoptotic rate increased in a dose dependent manner. Also, there was a dose-reaction relationship between B(a) P and CYP1A1 mRNA. The apoptotic rate of neural cell was positively correlated with CYP1A1 mRNA ( r =0.831, P <0.01) and CYP1A1 protein expression ( r =0.780, P <0.01). Conclusion B(a) P may induce apoptosis of neural cell, and CYP1A1 induction may be