Background: Borago officinalis and its derivatives are used in folk medicine to treat asthma because of its special effect on allergic disorders. It suppresses the tumor necrosis factor-alpha (TNF-alpha) and delivers gamma-linolenic acid. The objective of this clinical trial was to determine the effect of Borago officinalis on clinical and physiological findings in moderate persistent asthma. Materials and Methods: This prospective, randomized, double blind, placebocontrolled, clinical trial was conducted on patients aged 15-90 years with moderate asthma and forced expiratory volume in one second (FEV1) of 60-79% of predicted who presented to a sub-specialty clinic of pulmonary medicine. We randomly allocated subjects to receive either Borago extract (5 mL three times a day) or a matched placebo for one month. The primary outcome was the asthma control test (ACT) score and fractional exhaled nitric oxide (FENO) test. Secondary outcomes included clinical findings, spirometry, and sputum cytology including inflammatory cells. Results: Thirty-eight subjects with a mean age of 46.8±15.3 years and mean duration of asthma of 71±103 months were enrolled in our study. Cough, dyspnea, wheezing, nocturnal symptoms, and airway hyper-responsiveness reduced significantly in the Borago group after the treatment and ACT scores improved significantly (10.8±5.26 before and 15.4±5.12 after the trial). Flare up of asthma and emergency department visits in the Borago group also decreased significantly (3.6±2.33 to 2±1.86 flare ups per month and 0.62±0.9 to 0.05±0.23 for emergency department visits per month). Physiological parameters including spirometry, FENO, and sputum cytology including eosinophil and neutrophil did not change significantly. Conclusion: Borago improved the clinical findings of asthma, but it was not able to suppress the inflammation involved in asthma.