Tumor invasion into the extracellular matrix (ECM) and basement membrane (BM) is a crucial step of tumor metastasis. In order to investigate the possible therapeutic procedure for the tumor invasion, we investigated the anti-invasive activities of several synthetic serine protease inhibitors. FOY-305, a serine protease inhibitor, showed no cytotoxic activity against human HT-1080 fibrosarcoma cells at concentrations ranging from 0.1 to 100 micrograms/ml, while its analogs ONO-3403 and FO-349 showed slight cytotoxic activities at the concentration of 100 micrograms/ml. These compounds inhibited the activity of urokinase-type plasminogen activator (u-PA) which is one of serine proteases and considered to be associated with tumor invasion and metastasis in fibrin zymography. FOY-305 more potently inhibited the invasion of HT-1080 cells into the reconstituted BM Matrigel, as well inhibited u-PA activity, compared with ONO-3403 and FO-349. These results suggest that the anti-invasive activity of these compounds is consistent with their anti-fibrinolytic activities. In addition, the combined treatment of FOY-305 with FC-336 processing anti-invasive and anti-MMP properties resulted in marked enhancement of anti-invasive activity. In conclusion, FOY-305 inhibited the invasion of tumor cells through interference with the u-PA activity of tumor cells, and this inhibitory activity was augmented by the combination with a MMP inhibitor.