Purpose: The aim of this study is to evaluate the outcomes of pharmacological thromboprophylaxis given for short-term duration to the patients who underwent major abdominal surgery for colorectal and gastric cancer. Materials and Methods: This retrospective cohort study was performed in consecutive patients who underwent major abdominal surgery for colorectal and gastric cancer and received short-term pharmacological thromboprophylaxis during hospital stay were enrolled. Complete duplex ultrasonography of the lower limbs was performed for all patients to investigate both symptomatic and asymptomatic deep vein thrombosis (DVT). Results: Overall, 278 patients were evaluated for inclusion and 62 colorectal and 27 gastric cancer patients were enrolled. Of 89 patients, the incidence of total and symptomatic DVT was 4.5% and 2.2%, respectively. The patients with symptomatic DVT were diagnosed within the first four months. The incidence of coronary artery disease, mucinous adenocarcinoma and vascular tumor invasion were significantly higher in patients with DVT (P-values<0.001, 0.009, and 0.02, respectively). Conclusion Short-term pharmacological thromboprophylaxis after major abdominal surgery for colorectal and gastric cancer does not increase symptomatic DVT rates of patients with low Caprini score. Postoperative DVT surveillance may benefit patients with coronary artery disease, mucinous adenocarcinoma or vascular invasion of the tumor.