The inflammatory/anti‐inflammatory balance has an important role in the clinical course of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) (coronavirus disease [COVID‐19]) infection, which has affected over 200 million people since it first appeared in China in December 2019. This study aimed to determine the effectiveness of montelukast, which has known anti‐inflammatory and bronchodilatory effects, in these patients. The prospective randomized controlled study included 180 patients who were hospitalized in the infectious diseases department of our hospital between May and July 2021 and were diagnosed with the delta variant of SARS‐CoV‐2 by real‐time polymerase chain reaction of nasopharyngeal swabs. The patients were divided into three groups and received only standard treatment according to national guidelines (Group 1) or standard treatment plus 10 mg/day montelukast (Group 2) or 20 mg/day montelukast (Group 3). Laboratory parameters and pulmonary function tests (PFTs) at admission and on Day 5 of treatment were compared. Comparison of laboratory parameters on Day 5 showed that Groups 2 and 3 had significantly lower levels of lactate dehydrogenase, fibrinogen, D‐dimer, C‐reactive protein, and procalcitonin compared with Group 1 (p = 0.04, 0.002, 0.05, 0.03, and 0.04, respectively). In the comparison between Groups 2 and 3, only fibrinogen was significantly lower in Group 3 (p = 0.02). PFT results did not differ between the groups at admission, while on Day 5, only Group 3 showed significant improvements in forced expiratory volume in 1 s, forced vital capacity, and peak expiratory flow 25–75 compared with admission (p = 0.001 for all). Montelukast may be beneficial in COVID‐19 patients to maintain the inflammatory/anti‐inflammatory balance, prevent respiratory failure through its bronchodilator activity, and reduce mortality.