Introduction: COVID-19 is one of the most severe, intestinal, respiratory, and systemic infections in animals and humans. The purpose of this experiment was to evaluate the effect of kelofan syrup on biochemical factors and clinical signs of patients with COVID-19. Materials and Methods: This randomized clinical trial was performed on 60 hospitalized patients with moderate or severe COVID-19. The intervention group received 7.5 cc of kelofan syrup(a traditional Persian medicine product) every 12 hours for one week and the placebo group received 7.5 cc of placebo syrup. Serum levels of white blood cells (WBCs), C - reactive protein (CRP), lactate dehydrogenase (LDH), creatinine, lymphocyte, and clinical outcomes were measured before the beginning of the intervention and on day 7. Results: Kelofan syrup enhanced the white blood cell and reduced creatinine and LDH in the syrup group. However, serum levels of WBC, lymphocyte, CRP, LDH, and creatinine(P > 0.05) in the kelofan group at the end of the study did not significantly change than in the placebo group. Also, clinical outcomes such as fever, respiratory rate, saturated oxygen, cough, dyspnea, myalgia, duration of hospitalization, and fatigue did not change significantly from in the placebo group. Conclusion: our findings indicate that kelofan syrup for seven days could not alter biochemical and clinical outcomes than in the placebo group in patients with COVID-19. However, in some clinical symptoms such as cough, dyspnea, weakness, and biochemical factors like WBC, Cr, and LDH, a significant change was observed at the end of hospitalization in the intervention group.