Objective To investigate the clinical value of low molecular weight heparin (LMWH) as prophylaxis against venous thromboembolism after rectal cancer surgery.Methods The clinical data of 120 patients who received rectal cancer surgery at the Tianjin People's Hospital from October 2008 to October 2010 were retrospectively analyzed.All patients were divided into the test group (50 patients) and the control group (70 patients).Patients in the test group received subcutaneous injection of 0.4 ml of LMWH (4100 U) at 8-12 hours after operation,and then once a day thereafter until mobilization.LMWH was not given to patients in the control group.Patients in the 2 groups who experienced venous thromboembolism (VTE) and postoperative bleeding were recorded and compared.The clinical data of patients with VTE were proceeded with risk factors analysis.All data were analyzed using the t test,chi-square test or by calculating Fisher exact probability.All factors influencing VTE formation were analyzed using Logistic regression analysis.Results The incidences of VTE in the test group and the control group were 2.0％ (1/50) and 14.3％ (10/70),respectively,with a significant difference between the 2 groups (x2=3.915,P ＜ 0.05).The incidences of postoperative blood loss in the test group and the control group were 6.0％ (3/50) and 2.9％ (2/70),respectively,with no significant difference between the 2 groups (x2=0.149,P ＞ 0.05).Varicose veins of lower limbs,previous cardiopulmonary diseases,obesity and age ＞ 65 years were the independent risk factors of VTE (OR =2.3,2.5,1.4,2.1,P ＜0.05).The number of patients with VTE increased as the increase of the risk factors.Conclusion Early injection of LMWH after rectal cancer surgery is safe and effective in preventing VTE.