Background: Venous thromboembolism (VTE), consisting of deep vein thrombosis (DVT) and pulmonary embolism (PE), is the second-leading cause of death in patients with malignancy. P-selectin, the member of the selectin family of cell adhesion molecules, is found in the alpha granules of platelets and the Weibel-Palade bodies of endothelial cells. It is express on the cell surface on activation, mediates the adhesion of leukocytes, platelets, and cancer cells in inflammation, thrombosis, and cancer growth and metastasis. Recently, P-selectin has been investigated as a novel predictor for DVT. Objectives: To investigate the role of sP-selectin as predictors of DVT in cancer patients undergoing chemotherapy. Patients and Methods: This prospective cohort study was conducted in Dr. Kariadi hospital, Semarang, Indonesia, on 40 newly diagnosed cancer patients. Venous blood samples were drawn prior and after initial chemotherapy, for sP-selectin measurement with ELISA method. These patients were observed for the possibility of developing VTE during three-months period. Results: DVT occurred in 5 (12.5%) patients after a median period of 8 weeks. The most frequent cancer type was colorectal cancer (45%) and cervical cancer (15%). The cut-off point sP-selectin pre-and post- chemotherapy were 106,7 ng/ml and 111,7 ng/ml respectively. The median levels of sP-selectin in DVT patients pre-chemotherapy was 121.0ng/ml (IQR 107.5-230.6) and post-chemotherapy was 204.4ng/ml (IQR 110.9-278.3). In other hand, the median levels of sP- selectin pre-chemotherapy and post- chemotherapy in DVT negative patients were 82.0ng/ml (IQR 31.3-230.6) and 92.5 (IQR 40.9-278.3), respectively. With cut-off point sP-selectin level 111,7 ng/ml, the relative risk of DVT event was 8,7 (95% CI 1,017-74,39). Conclusion: In this study, high plasma levels of s P-selectin are predictive for venous thromboembolism in cancer patients undergoing chemotherapy.