Abstract: ObjectiveTo investigate the effects and mechanisms of B(a)Pon P53,P21 and AhR pathway of HELF cells in vitro.MethodsDifferent doses of α-NF,AhR an tagonist were used to pre-treat human diploid lung fibroblast (HELF)cells for 1h,followed by B(a)Ptreatment for additional 2h with or without S₉,or followed by B(a)P treatment for additional 24h without S₉.The prote in levels of P53,P21 were detected by western blot to investiga te AhR pathway's role involving in the effects of B(a)P on P53,P21.ResultsPre-treatment with α-NF at doses of 2.5 mol/L or 5.0 mol/L could reverse the increase of P53 levels with B(a)P treatment for 2h without or with S₉,respectively.Pre-treatment with α-NF at doses of 2.5 mol/L and 5.0 mol/L could reverse the increase of P53 levels with B(a)Ptreatment for 24h without S₉.Pre-treatment with α-NF at doses of 2.5 mol/L and 5.0 mol/L could reverse the increase of P21 levels with B (a)Ptreatment for 24h without S₉.ConclusionP53,P21 play important roles in the response of HELF to DNA damage in duced by B(a)P,in which AhR pathway takes part in there sponse.