Background: The COVID-19 pandemic necessitated exploration of convalescent plasma (CP) therapy. This phase-II RCT evaluated CP's efficacy in 30 severe COVID-19 patients (June 2020–July 2021), comparing standard care (n=30) with CP-added therapy (n=30). Despite historical success in viral outbreaks, evidence remained conflicting. We assessed 28-day mortality, clinical improvement, and safety, addressing gaps in donor antibody variability and timing. Objective: To determine therapeutic Role of Convalescent Plasma (CP) therapy in the treatment of severe COVID-19. Methods and Procedure: It was a Randomized Controlled phase-II Trial which was carried out at COVID-19 unit and ICU Bangabandhu Sheikh Mujib Medical University, Dhaka from 01June 2020 to 31July 2021. Plasma was collected and supplied in the department of Transfusion Medicine of BSMMU and transfused in patient at ICU, BSMMU. After proper evaluation 30 healthy donors required amount of convalescent plasma of COVID-19 was collected by continuous flow cell separator. The collected convalescent plasma was transfused to; 30 (INTERVENTION ARM) severe ill patients receiving standard treatment protocol admitted in ICU, BSMMU, Dhaka. Then the improvement of these patients was observed and another 30(control) patients receiving standard treatment protocol only and comparison was made. Before administration of the plasma it was screened for RCT-PCR for covid-19. HBsAg, Anti-HCV, HIV and other infections. Results: The study included 60 COVID-19 patients (30 control, 30 intervention) with comparable baseline characteristics (mean age 51-53 years; 40% vs. 56.6% males). The intervention group showed significantly higher baseline D-dimer (4.3 vs. 0.5 µg/mL, p<0.001) and ferritin (1045 vs. 631 ng/mL, p=0.049). Both groups had similar 28-day mortality (26.6%, RR=1.00, p=0.95), hospitalization duration (10 vs. 9 days), and discharge rates (63.3%). Clinical parameters improved over time, with mortality declining from 7.1% (Week-I) to 4.5% (Week-IV). Conclusion: In conclusion, this phase-II randomized controlled trial demonstrated that convalescent plasma (CP) therapy did not significantly improve 28-day mortality or other clinical outcomes in severe COVID-19 patients compared to standard care alone.