As an anticytokine therapy, tocilizumab has been recommended for the management therapy in patients with severe and serious COVID-19 cases. The association between the severity of COVID-19 and blood groups has been the subject of prior research. Therefore, it is important to analyze the relationship between blood types and the effectiveness of tocilizumab (TCZ) therapy in COVID-19 patients. This research involved 68 patients diagnosed with severe and critical COVID-19 receiving Tocilizumab (TCZ) therapy at Universitas Indonesia Hospital. Blood type O was associated with a significantly improvement in CRP levels (P=0.014) and has better favorable outcomes compared to other blood type in terms of WHO Clinical Progression Scale (OR: 1.254, 95% CI: 0.457-3.443; P=0.797), length of stay (OR: 5,333, 95% CI: 0.495-3,734; P=0.614), and improvement in CRP levels (OR: 5,333, 95% CI: 1.385-20,541; P=0.014). © 2023 by Faculty of Pharmacy, Mahidol University, Thailand is licensed under CC BY-NC-ND 4.0. To view a copy of this license, visit https://www.creativecommons.org/licenses/by-nc-nd/4.0/