AIM: To determine the role and effect of nitric oxide synthase type Ⅱ (NOSⅡ) in cirrhotic rats.METHODS: Expression of NOSⅡ mRNA was detected by real time RT-PCR. The activity of nitric oxide synthase and serum levels of NO, systemic and portal hemodynamics and degrees of cirrhosis were measured with high sensitive methods. Chinese traditional medicine tetrandrine was used to treat cirrhotic rats and to evaluate the function of NO.Double-blind method was applied during the experiment.RESULTS: The concentration of NO and the activity of NOS were increased markedly at all stages of cirrhosis, and iNOSmRNA was greatly expressed. Meanwhile the portalvenous-pressure (PVP), and portal-venous-flow (PVF) were significantly increased. NO, NOS and iNOSmRNA were positively correlated to the quantity of hepatic fibrosis.Tetrandrine significantly inhibited NO production and the expression of iNOSmRNA.CONCLUSION: Increased hepatic expression of NOSⅡ is one of the important causes of hepatic cirrhosis and portal hypertension.