The formation of a thrombus is a key event in thromboembolic disorders, that contribute to high mortality and morbidity in affected patients. In the present study, we synthesized a library of novel substituted 3,3-dibutyl-8-methoxy-2,3-dihydrobenzo [b] [1,4] thiazepin-4(5H)-one derivatives which were tested for their platelet aggregation and thrombin inhibitory activity. Among the tested compounds, 3,3-dibutyl-7-(2-chlorophenyl)-8-methoxy-2,3-dihydrobenzo[b] [1,4]thiazepin-4(5H)-one (DCT) displayed the maximum thrombin inhibition with an IC50 value of 3.85 μM and thus DCT was chosen for further studies. Next, the effect of DCT on primary hemostasis was evaluated using agonist-induced platelet aggregation model. The lead compound inhibited the collagen- or ADP- or thrombin-induced platelet aggregation in a dose-dependent manner. Furthermore, DCT prolonged the process of clot formation when evaluating plasma re-calcification time (320 ± 11 sec at 5 µg DCT), activated partial thromboplastin time (58.0 ± 0.01 sec at 2 µg), and prothrombin time (14.7 ± 0.01 sec at 5 µg). Molecular docking studies suggested that the benzothiazepinones evaluated here consistently display hydrogen bonding with Ser214 of thrombin, which is similar to that of the co-crystallized ligand (1-(2R)-2-amino-3-phenyl-propanoyl-N-(2,5dichlorophenyl)methylpyrrolidine-2-carboxamide). DCT displayed additional hydrogen bonding to Ser195 and π-π interactions between its methoxyphenyl groups and Trp60, thereby providing a structural rationale for the observed biological effect.