Objective: To investigate the effects of vitamin D drops on immune function in children with recurrent respiratory tract infections (RRTI). Methods: The clinical data of 119 children with RRTI in our hospital were retrospectively retrieved, and they were divided into group A (n=59, receiving routine treatment) and group B (n=60, receiving vitamin D drops) based on their treatment modality. The clinical efficacy, symptom disappearance time, immune function index, insulin-like growth factor (IGF-1), 25-hydroxyvitamin D(3) [25-(OH)D(3)], serum y-interferon (INF-y), and the number of episodes of respiratory tract infections were compared between the two groups. Results: The total effective rate of treatment in group B was 96.67%, which was significantly higher than 71.19% in group A (P