© 2021 Ankara Yildirim Beyazit University. All Rights Reserved.Objectives: A hypercoagulability status has been reported in SARS-CoV-2 infection. Beside their traditional roles, platelets are referred to as immune cells. The purpose of the study was to examine platelet activation and aggregation in COVID-19. Materials and Methods: This case-control study comprised 61 patients with SARS-CoV-2 infection and 18 healthy individuals. The patients were separated into groups with respect to the need for treatment in the intensive care unit (ICU). CD41, CD61, CD42a, and CD42b were determined as platelet activation markers, and platelet aggregation tests were analyzed in all groups. Results: Platelet CD41, CD61, CD42a, and CD42b expressions were significantly elevated in ICU patients compared to non-ICU patients and healthy donors. Patients in the ICU group had increased platelet aggregations than those in non-ICU patients and controls. Additionally, platelet activation and platelet function tests correlated with inflammatory and coagulation markers involving C-reactive protein, Interleukin-6, neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio, monocyte to lymphocyte ratio, D-dimer, and fibrinogen concentrations. Conclusion: Enhanced platelet activity and faster platelet aggregation were observed in ICU COVID-19 patients. It is possible that platelet hyperreactivity may contribute to the progression of SARS-CoV-2 infection. The relationships between platelet activation and functions tests with inflammatory and coagulation markers show that systemic inflammation and cytokines may trigger the hypercoagulability in COVID-19 patients in ICU, or hyperactivated platelets could augment the inflammation.