Coronavirus disease 2019 (COVID-19) pandemic has caused an urgent need for investigating potential treatments. Traditional medicine offers many potential remedies that have been historically used and have the advantage of bypassing the cultural obstacles in the practice of medicine. We aimed to investigate the efficacy of Zufa syrup in the treatment of suspected patients with mild to moderate symptoms of COVID-19. This triple-blind randomized controlled trial recruited patients with evidence of COVID-19 on chest computed tomography without an indication of hospital admission from March 2020 until April 2020. Participants were assessed by a physician and completed a pre-specified form to assess the duration and severity of symptoms. Patients were randomized to receive Zufa syrup (a combination of herbal medicines: Nepetabracteata, Ziziphus jujube, Glycyrrhizaglabra, Ficuscarica, Cordia myxa, Papaver somniferum, Fennel, Adiantumcapillusveneris, Viola, Viper‘s-buglosses, Lavender, Iris, and sugar) or identical-looking placebo syrup at a dose of 7.5 mL (one tablespoon) every 4 hours for 10 days. After applying the eligibility criteria, 116 patients (49.1% male) were randomized to trial arms with a mean age of 44.3. During the follow-up, Cough, dyspnea, headache, myalgia, anorexia, anxiety, and insomnia improved gradually in both groups, and showed no difference between Zufa syrup and placebo. Oxygen saturation and pulse rate had stable trends throughout the follow-up and were similar between study arms. No patient required hospital admission or supplemental oxygen therapy during the study period. To conclude, in patients with mild to moderate symptoms of COVID-19, Zufa syrup did not show any difference in symptomatology over a 10 days’ period when compared with placebo. Due to potential effects of medicinal plants in the treatment of respiratory infections, further studies are warranted to clarify their role in COVID-19. The study was approved by the Ethics Committee of the Qom University of Medical Science (Ethics committee reference number IR.MUQ.REC.1398.165) on March 10, 2020 and was registered in Iranian Clinical Trial Center (approval ID: IRCT20200404046934N1) on April 13, 2020.