Objective: To study the changes of expressions of nitric oxide synthase (NOS) of the constitutive type (cNOS) and inducible type (iNOS), the apoptosis related genes bax and bcl 2, as well as the tumor necrosis factor (TNF α) in immunological liver injury (ILI) and to explore the preventive effects of Angelica sinensis polysaccharide (ASP) on ILI and its mechanism in mice.Methods: ILI model mice induced by intraperitoneal injection of lipo polysaccharide (LPS) and BCG vaccine were treated with ASP of different doses (30mg/kg, 60mg/kg) by gastrogavage every day for 7 days. The serum alanine transaminase (ALT) and glutathione S transferase (GST) activities and NO content in the liver were detected; the expressions of cNOS, iNOS, bcl 2, bax were assessed with immuno histochemical method, and the TNF α mRNA expression in the liver was observed by reverse transcriptase polymerase chain reaction (RT PCR).Results: Compared with the normal mice , the NO production and ALT, GST levels were raised significantly in the model mice, the TNF α mRNA expression was also raised significantly. But no obvious changes of cNOS was found. Small dose ASP (30mg/kg) could reduce NO production and ALT, GST levels in model mice by 19.5%, 23.7% and 40.0% respectively, decrease the expression of iNOS and bax by 48.3%, and 26.4%, and increase the expression of cNOS, bcl 2 by 66.9% and 337.3%, respectively, but it could not reduce the TNF α mRNA expression in the liver. Large dose of ASP (60mg/kg) was not more effective than that of small dose.Conclusion: Changes of NO production and TNF α mRNA may play an important role in ILI. The mechanism of ASP in intervening ILI may be through modulation on cNOS, iNOS, bax, bcl 2 expression to block the damage of BCG vaccine and LPS on hepatocytes. Objective: To study the changes of expressions of nitric oxide synthase (NOS) of the constitutive type (cNOS) and inducible type (iNOS), the apoptosis related genes bax and bcl 2, as well as the tumor necrosis factor (TNF α) in Immunological liver injury (ILI) and to explore the preventive effects of Angelica sinensis polysaccharide (ASP) on ILI and its mechanism in mice.Methods: ILI model mice induced by intraperitoneal injection of lipo polysaccharide (LPS) and BCG vaccine were treated with ASP of Different doses (30mg/kg, 60mg/kg) by gastrogavage every day for 7 days. The serum alanine transaminase (ALT) and glutathione S transferase (GST) activities and NO content in the liver were detected; the expressions of cNOS, iNOS, Bcl 2, bax were assessed with immuno histochemical method, and the TNF α mRNA expression in the liver was observed by reverse transcriptase polymerase chain reaction (RT PCR).Results: Compared with the normal mice, the NO production and ALT, DST levels were raised significantly in the model mice, the TNF α mRNA expression was also raised significantly. But no obvious changes of cNOS was found. Small dose ASP (30mg/kg) could reduce NO production and ALT, GST levels in model mice by 19.5%, 23.7% and 40.0% respectively, decrease the expression of iNOS and bax by 48.3%, and 26.4%, and increase the expression of cNOS, bcl 2 by 66.9% and 337.3%, respectively, but it could not reduce the TNF α mRNA expression in the liver. Large dose of ASP (60mg/kg) was not more effective than that of small dose.Conclusion: Changes of NO production and TNF α mRNA may play an important role in ILI. The mechanism of ASP in intervening ILI may be through modulation on cNOS, iNOS, bax, bcl 2 expression to block the damage of BCG vaccine and LPS on hepatocytes.