On day 9, the arterial blood gas analysis showed PaO2/FiO2 of 86, consistent with severe ARDS. Intravenous methylprednisolone (1 mg/kg/day daily) was started. On day 10, convalescent plasma was obtained from a male donor in his 20s who had recovered from COVID-19 for 21 days. He was diagnosed as COVID-19 presenting fever, cough and pneumonia, however, showed complete recovery and didn’t have any symptom at the time of plasma donation. He has met the blood donor eligibility criteria for plasma donation, including age, weight, reasonable-sized antecubital veins. Also, allogeneic donor screening tests, defined by enforcement rules of the Blood Management Act in Korea, were acceptable for transfusion. Donor apheresis was performed with Spectra Optia apheresis system (CMNC software; Spectra Optia IDL Tubing set; Terumo BCT, Lakewood, CO, USA), 500 mL of convalescent plasma was collected. Anti-SARS-CoV-2 IgG antibody in plasma was measured by enzyme-linked immunosorbent assay (ELISA) (Novel Coronavirus COVID-19 IgG ELISA kit; Epitope Diagnostics, San Diego, CA, USA) and optical density (OD) ratio for IgG was 0.586 (cut-off value 0.22). The plasma was divided into two doses and administered to the patient at 12 hours interval. Each dose was given over for 1 hour. No adverse reaction occurred after the administration of convalescent plasma.