Objective:To survey the incidence of deep venous thrombosis (DVT) in high risk patients undergoing thoracotomy and observe the changes of hemostatic activity. Methods: Fifty-two consecutive patients (ages that ranged from 35 to 79, 34 men and 18 women) with lung or esophagus cancer were enrolled into this prospective trial. The patients included underwent major thoracic surgery from February 2003 to April 2003. Bilateral lower extremity duplex ultrasonography for DVT screening was performed 3-10 days post surgery in all 52 patients and 57 matched clinic normal controls. Venous blood was collected to determine fibrinogen(FIB), D-dimer(D-D), plasminogen activator inhibitor (PAI), antithrombin (AT), thrombin antithrombin complex (TAT), prothrombin time (PT),international normalized ratio(INR), and activated partial thromboplastin time (APTT) immediately before surgery, the third and tenth days postoperatively. No patient had a prior thromboembotic history. Risk factors for DVT were evaluated. Results: Of the 52 patients, 28 (53.8%) had an acute postoperative DVT detected in the calf. One patient died of suspected pulmonary embolism postoperatively. Plasma levels of FIB and D-D increased significantly up to 7 d after operation. AT level decreased significantly 3 d after operation and returned to normal 7 d latter. TAT increased significantly 3 d post operation and decreased to normal on day 7. PAI level was lowered 3 d after surgery, but increased significantly on day 7 compared with that on day 3. With the addition of risk factors related to thrombosis, the incidence of DVT was increased correspondingly. Conclusion: Of the patients undergoing major thoracic surgery,53.8% of them had a postoperative DVT by postoperative screening duplex ultrasound. In Chinese population, incidence of DVT appears to be high without prophylaxis, which is similar to other reports of westerners. These patients had a number of risk factors for the development of DVT, which include older age, overweight, hypertension, diabetes, and history of thromboembolism, etc. Prophylactic measures should be taken against postoperative venous thromboembolism in major thoracic surgery with high risk, including early mobilization, anticoagulant therapy with heparins, and intermittent pneumatic compression (IPC).