Recombinant human severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) monoclonal antibody JS016 showed neutralizing and therapeutic effects in preclinical studies. The clinical efficacy and safety of the therapy needed to be evaluated. In this phase2/3, multicenter, randomized, open-label, controlled trial, hospitalized patients with moderate or severe coronavirus disease 2019 (COVID-19) were randomly assigned in a 1:1 ratio to receive standard care or standard care plus a single intravenous infusion of JS016. The primary outcome was a six-level ordinal scale of clinical status on 28 days since randomization. Secondary outcomes include adverse events, 28-day mortality, ventilator free days within 28 days, length of hospital stay, and negative conversion rate of SARS-CoV-2 nucleic acid on day 14. A total of 199 patients were randomized, and 197 (99 in JS016 group and 98 in control group) analysed. Most patients, 95 (96%) in JS016 group and 97 (99%) in control group, were in the best category on day 28 since randomization. The odds ratio of being in a better clinical status was 0.31 (95% confidence interval [CI], 0.03-3.19; p = 0.33). Few adverse events occurred in both groups (3% in JS016 group and 1% in control group, respectively; p = 0.34). SARS-CoV-2 neutralizing antibody JS016 did not show clinical efficacy among hospitalized Chinese patients with moderate to severe COVID-19 disease. Further studies are needed to assess the efficacy of the neutralizing antibody to prevent disease deterioration and its benefits among groups of patients specified by disease course and severity. (This study has been registered at ClinicalTrials.gov under identifier NCT04931238.).