This study sought to evaluate the treatment effect of montelukast in children with obstructive sleep apnea (OSA) after tonsillectomy and/or adenoidectomy (T&A). Fifty-eight children with persistent OSA after T&A were included and randomly divided into 2 groups: one group was administered montelukast for 12 weeks, and the other received no treatment. Clinical information, such as the apnea-hypopnea index (AHI) and nadir oxyhemoglobin saturation (nadir SpO2), was recorded. Symptoms of OSA were evaluated using the validated Pediatric Sleep Questionnaire (PSQ). After surgery, there was no difference in terms of AHI, nadir SpO2, and PSQ scores between 2 groups. After the 12-week course of montelukast administration, the treatment group had significant improvement in the AHI, nadir SpO2, and PSQ scores (P < .001), while the no-treatment group had no change over time (P > .05). In summary, montelukast as a complementary therapy can improve sleep disturbances in children with OSA after T&A.