OBJECTIVE: To determine the effect of Salviae miltiorrhizae on cirrhosis and portal hypertension by inhibiting nitric oxide synthase type II (NOSII) in rats. METHODS: Real time RT-PCR was used to detect the expression of NOSII mRNA. The enzymatic activity of nitric oxide synthase and the circulating levels of nitric oxide (NO), systemic and portal hemodynamics, and quantification of cirrhosis were measured with highly sensitive methods. Traditional Chinese medicine was utilized to treat cirrhotic rats and the function of NO was evaluated. Double-blind method was applied in the experiment constantly. RESULTS: The concentration of NO increased markedly at all stages of cirrhosis, and so did the enzymatic activity of NOS, and the iNOSmRNA expressed greatly. Meanwhile the portal-venous-pressure (PVP), portal-venous-flow (PVF) increased significantly. NO, NOS and iNOSmRNA were positively correlated to the quantity of hepatic fibrosis. Salviae miltiorrhizae significantly inhibited NO production and inhibited the expression of iNOSmRNA. CONCLUSIONS: The increased hepatic expression of NOSII is one of the important factors causing cirrhosis and portal hypertension. Salviae miltiorrhizae significantly ameliorates cirrhosis and portal hypertension.