Introduction: The use of convalescent plasma (CP) transfusions is very valuable in the current COVID-19 outbreak, given that there are no specific preventive and therapeutic options. Materials and methods: 50 patients with severe COVID-19 disease treated with convalescent plasma transfusion were included in the study. The efficacy of CP and in which situations it was effective were investigated. Conclusion: 80 % of the patients recovered, and 20 % died in our study. The mean age of the patients who died was found to be higher than the patients who recovered. CRP, ferritin, D-dimer, neutrophil, MPV, and NLR counts were found to be higher, and lymphocyte and platelet counts were lower in the deceased group after CP. It was determined that patients who received CP within the first five days were hospitalized for a shorter period. Discussion: Administration of CP transfusion within the first five days in severe COVID-19 patients has been shown to reduce hospital stay length.