Patients with portal vein thrombosis, who have chronic liver diseases especially liver cirrhosis associated with low levels of AT III, will receive intravenous injection of NPB-06 or placebo. The superiority of NPB-06 to placebo as anticoagulative agent will be verified in a randomized, double-blind, parallel-assignment design based on the proportion of patients obtained complete recanalization or partial recanalization of portal vein thrombosis.