The purpose of this study was to evaluate the changes in plasma soluble fibrin (SF) levels over time in gynecologic cancer patients following surgery. Furthermore, we examined the duration of the coagulation stage and determined a suitable duration for which thromboprophylaxis with anticoagulant agents should be administered. We retrospectively studied 311 patients with invasive gynecologic cancer who underwent surgery at Okayama University Hospital, Japan. The plasma SF levels were measured serially prior to the operation and on postoperative days 0, 1, 3, 5, 7, 10, 14, 21 and 28. The plasma SF levels increased rapidly, peaked on postoperative day 1 and then decreased. The SF levels of patients with venous thromboembolism (VTE) were significantly different from those of VTE-negative patients on postoperative days 0-10. The SF levels on each day did not significantly differ between patients treated with chemical anticoagulants and those treated mechanically. The plasma SF levels were elevated (≥7.0 μg/ml) in 159 of the 311 patients (51.1%) on one of the days when these levels were measured. Among the patients with elevated plasma SF levels, 110 patients (69.2%) peaked on days 0-3 and only 9 patients (5.7%) peaked on days 21-28. Although only 1 of the 14 patients (7.1%) who showed peak levels on day 14 had undergone chemotherapy following surgery, 8 of the 9 patients (88.9%) whose levels peaked on days 21-28 had undergone chemotherapy following surgery (P= 0.0002). In conclusion, the plasma SF levels increased rapidly, peaked on postoperative day 1 and then decreased. These levels peaked within 14 days of surgery in most cases. Therefore, chemical thromboprophylaxis may be administered for at least up to 14 days following surgery.