Background: Respiratory diseases remain among the top five leading causes of morbidity, with an incidence rate of 788.4 cases per 10,000 population in 2021. Among these, acute bronchitis accounts for 9.3%. According to international clinical guidelines for the diagnosis and treatment of adult acute bronchitis, symptoms usually resolve spontaneously within 1–3 weeks, but they considerably reduce the patient’s quality of life. Therefore, Colsaurin syrup, a new natural formulation with analgesic and anti-inflammatory effects, was clinically investigated to assess its efficacy and safety. The introduction of this domestically produced herbal medicine into clinical practice is expected to have both medical and socioeconomic significance by expanding the range of national pharmaceutical products. Aim: To evaluate the effect of Colsaurin syrup on the quality of life in adults diagnosed with acute bronchitis. Materials and Methods: This study was a randomized, double-blind, placebo-controlled clinical trial conducted among inpatients at Songinokhairkhan District General Hospital, Ulaanbaatar. Adult patients diagnosed with acute bronchitis (J20) who met the inclusion criteria and provided informed consent were enrolled. Participants were randomly assigned to either the Colsaurin or placebo group. Result: In the Bronchitis Severity Score (BBS) assessment, baseline mean scores indicated severe disease: 10.88±2.47 in the Colsaurin group and 10.67±2.16 in the placebo group. After treatment, scores decreased significantly to 3.50±1.41 (p<0.001) in the Colsaurin group and 5.00±2.24 (p=0.006) in the placebo group, indicating greater improvement in the Colsaurin-treated patients. In the Visual Analog Scale (VAS) assessment, the mean pre-treatment score for both groups was 7, corresponding to frequent cough, which decreased to 2 after treatment (p<0.05), representing a 28% reduction in coughing discomfort. In the Cough and Sputum Assessment Questionnaire (CASA-Q), the Colsaurin group showed a 3.25-point reduction after treatment, indicating a significant decrease in cough frequency and triggering factors (p<0.05). Conclusion 1. In patients diagnosed with acute bronchitis (J20), treatment with Colsaurin syrup reduced disease severity by 30% and alleviated cough-related discomfort by 28% compared to baseline. 2. Moreover, patients reported improved sleep quality and work capacity, reflecting an overall enhancement in quality of life. 3. No adverse effects were observed in the Colsaurin treatment group.