Currently, there are no effective treatments for novel corona virus disease 2019 (COVID-19). In this study, we report the preliminary results on the efficacy and safety of convalescent plasma (CP) infusion, as monotherapy in 9 patients with severe COVID-19 disease. The median time from symptom onset to CP transfusion was 6 days. All symptoms improved significantly after a median of 8 days. In 6/9 patients, symptomatic improvement was observed already after the 1st dose of CP transfusion. Laboratory parameters associated with disease severity tended to significantly decrease over time and lymphocyte counts significantly increased on day 14. All patients exhibited significant increases in SARS-CoV-2 IgA and IgG antibodies starting on day 7 through day 21 after CP infusion with concurrent reduction of SARS-CoV-2 RNA on days 7 and 14 with 44.4% % of the patients having undetectable SARS-CoV-2 RNA on day 14. After a median follow-up of 66 days, all patients remain alive. Eight patients recovered completely and were discharged from hospital after a median duration of hospitalization of 21 days. No severe adverse events were observed. In conclusion, this preliminary report suggests that CP infusion monotherapy administered early in the disease course may be a safe and effective strategy for patients with severe COVID-19 disease. Trial registration: NCT04408209. Registered 05 May 2020- Retrospectively registered, (https://clinicaltrials.gov/ct2/show/NCT04408209?term=NCT04408209&draw=2&rank=1).