Thrombomodulin (TM) has multiple biological functions and modulates not only anti-coagulation, but also cell proliferation, adhesion, and anti-inflammation activities. The main function of TM is to activate the anticoagulant pathway of protein C. Soluble TM is related to metastasis by its inactivation of thrombin.To clarify the correlation between serum TM levels and clinicopathological parameters.The plasma TM levels (FU/ml) of 135 primary soft tissue tumors (benign, 67; soft tissue sarcoma (STS), 68) were measured before biopsy or treatment. TM levels were analyzed and compared to various clinicopathological parameters. Log-rank test and Cox proportional analysis were used to evaluate recurrence-free survival, metastasis-free survival, and overall survival.STS tumors had significantly higher TM values (15.9) than benign tumors (13.7) (p= 0.0138). 5-year MFS was 81.1% in low TM and 40.0% in high TM (p= 0.00671), and 5-year OS was 85.5% in low and 52.5% in high TM in grades 1-3 (p= 0.0673). In multivariate COX proportional analysis, high-TM showed a significant difference (MFS: HR 4.37, p= 0.0147; OS: HR 3.60, p= 0.0557) in grades 1-3.We demonstrated that a high level of soluble TM has the potential to be a significant predictor of metastasis and poor prognosis in STS patients. TM is a candidate molecular marker for high metastatic potential and can be clinically useful for guiding therapeutic strategy.