Platelets are attributed an increasing role in the post-traumatic immune response. The exact mechanisms, particularly the link between immune response and hemostasis, have not been conclusively established. This study aimed to investigate the activity marker CD63 on platelets after polytrauma and its significance for hemostasis. A non-interventional, prospective clinical study was conducted, in which the blood of 20 polytraumatized patients was analyzed at nine time points within 10 days following trauma. Peripheral blood platelets were analyzed using flow cytometry to determine CD63 expression and rotational thromboelastometry (ROTEM^®) for hemostatic platelet function. Additionally, the clinical parameters of age, gender, and injury severity were correlated to the experimental outcomes. During the observation period, an increase in platelet count and CD63 expression was observed. Simultaneously, a hemostasiological dysfunction with reduced platelet maximum clot firmness (MCF) was observed. The factors of age, gender, and injury severity showed no significant influence on immunological activation or coagulation function. These results suggest that polytrauma induces a platelet response and CD63 activation while simultaneously impairing hemostasis. This reveals a novel perspective on post-traumatic coagulation disorders, indicating that immunologically active platelets may lose their ability to contribute effectively to blood clotting. Consequently, these findings emphasize the critical role of platelet immunology in hemostatic regulation.