We recently reported that inhibitors against human dihydroorotate dehydrogenase(DHODH)have broad-spectrum antiviral activities including their inhibitory efficacies on SARS-CoV-2 replication in infected cells.However,there are limited data from clinical studies to prove the application of DHODH inhibitors in Coronavirus disease 2019(COVID-19)patients.In the present study,we evaluated Leflunomide,an approved DHODH inhibitor widely used as a modest immune regulator to treat autoimmune diseases,in treating COVID-19 disease with a small-scale of patients.Cases of 10 labo-ratory-confirmed COVID-19 patients of moderate type with obvious opacity in the lung were included.Five of the patients were treated with Leflunomide,and another five were treated as blank controls without a placebo.All the patients accepted standard supportive treatment for COVID-19.The patients given Leflunomide had a shorter viral shedding time(median of 5 days)than the controls(median of 11 days,P = 0.046).The patients given Leflunomide also showed a significant reduction in C-reactive protein levels,indicating that immunopathological inflammation was well controlled.No obvious adverse effects were observed in Leflunomide-treated patients,and they all discharged from the hospital faster than controls.This preliminary study on a small-scale compassionate use of Leflunomide provides clues for further under-standing of Leflunomide as a potential antiviral drug against COVID-19.