Objective:To screen the high performance,specific and nontoxic anti HBV antisense oligonucleotide fragment.Methods:Taking 2.2.15 cells as cell model,the antisense oligodeoxynucleotides(ASON)toward the HBV regulation genesenhancerⅡ(HBV EFⅡ)were designed and synthesized.The role played by ASON in inhibiting the secretion and expession of HBsAg and HBeAg by the host cells was detected by ELISA method.The effect of ASON on prolifezation and metabolism of the cells was detected by MTT method.Results:The inhibitory rate of HBsAg by ASON was 92% and 75%,respectively,indicating that itsdifference from that of noncomplementary sequence control group(inhibitory rate was 11%)had considerable statistical significance( P 0.05).Conclusion:ENⅡ is one of the most important target oriented sequencial selective regions of research on anti HBV nature of antisense oligonucleotide.