Mechanical heart valve replacement (MHVR) entails lifetime oral anticoagulation to eliminate thrombosis. However, adverse events may still occur despite proper anticoagulation therapy. In this study, we investigated whether D-dimer can predict the clinical events in post-MHVR patients during oral anticoagulation therapy. This was a single-center, prospective study. In all, 772 patients who underwent MHVR in the Wuhan Asia Heart Hospital from January 2013 to May 2014 were screened. Patients were assigned to the abnormal D-dimer group and the normal D-dimer group according to the D-dimer levels measured 3 months after the beginning of the oral anticoagulation therapy regime. All patients were followed up for 24 months or until the observation of the endpoints, which included thrombotic events, bleeding events, and all-cause deaths. A total of 718 patients were included in the analysis: 91 had abnormal D-dimer levels, and 627 had normal D-dimer levels. In all, 53 events were observed during 24 months. Compared with the normal D-dimer group, patients with abnormal D-dimer levels had a higher incidence of thrombotic events (10 versus 14; hazard