Objective To investigate the efficacy and safety of preventive anticoagulant therapy at different time windows on formation of portal vein thrombosis after laparoscopic splenectomy and pericardial devascularization.Methods The study was performed as a randomized,prospective trial.83 patients with portal hypertension who underwent laparoscopic splenectomy and pericardial devascularization were divided into four groups:the non preventive anticoagulant group (n =21),the prophylactic anticoagulant group (n =23),the 24 hours of preventive anticoagulant group (n =19) and the 48 hours of preventive anticoagulant group (n =20).The incidences of postoperative portal vein thrombosis,the Yerdel grading,platelet count,APTT,and bleeding complications were studied.Results The incidences of portal vein thrombosis in the four groups were 100％,39.1％,47.3％,55％,respectively,and the difference among the 4 groups was significantly different (P ＜ 0.05).The incidences of portal vein thrombosis between the prophylactic anticoagulant group and the 24 hours of preventive anticoagulant group showed no significant difference (P ＞0.05),but the incidences of portal vein thrombosis after 48 hours of preventive anticoagulant group was significantly higher than the prophylactic anticoagulant group and the 24 hours of preventive anticoagulant group,respectively (P ＜ 0.05).Postoperative bleeding complications,platelet count and APTT after the operations showed no significant differences (P ＞ 0.05).However,the plasma level of D-dimer in the non preventive anticoagulant group was significantly higher than the preventive anticoagulant group (P ＜ 0.05).Conclusion Preventive anticoagulant therapy effectively reduced the incidence of portal vein thrombosis after laparoscopic splenectomy and pericardial devascularization,but it did not significantly increase the risk of postoperative bleeding complications.