Background Pulmonary infection is a common complication in pediatric living donor liver transplantation (LDLT) recipients. It has been suggested that vitamin D has a role in immune defense against infection. Therefore, we investigated the effect of preoperative serum 25-hydroxyvitamin D-3(25(OH)D-3) on the risk of pneumonia in hospitalized patients undergoing LDLT. Materials and Methods This study was a retrospective review of patient records. Fifty consecutive pediatric patients (aged < 14 years) who underwent LDLT from January 2017 to December 2017 were included. Pulmonary infection in the early postoperative period was diagnosed using clinical, radiological, or laboratory criteria. Preoperative serum 25(OH)D(3)level, demographic characteristics, primary diagnosis, ascites, time to extubation, length of intensive care unit stay, and perioperative laboratory values were recorded. Vitamin D deficiency, insufficiency, and sufficiency were defined as a serum 25(OH)D(3)concentration of less than 10, 10 to 20, and more than 20 ng/mL, respectively. Associations between serum 25(OH)D(3)levels and pulmonary infection were analyzed. Results Of 50 pediatric patients who underwent LDLT, 19 (38%) developed pulmonary infections in the early postoperative period. The mean serum 25(OH)D(3)level in these subjects was 18.7 +/- 17.2 ng/mL (range, 3.0-70.0 ng/mL). Twenty patients (40%) had severe vitamin D deficiency (<10 ng/mL). The mean serum 25(OH)D(3)level was significantly decreased (9.3 +/- 7.4 vs 24.5 +/- 19.1 ng/mL,P = .002) in patients with pulmonary infection compared with those without pulmonary infection. Serum 25(OH)D(3)level as a continuous variable (odds ratio [OR], 0.90, 95% confidence interval [CI], 0.84-0.97,P = .008) and a classification variable (<= 10 ng/mL) (OR, 7.42, 95% CI, 2.06-26.79,P = .002) were significantly associated with pulmonary infection in univariate analysis. After adjusting for other significant predictors (age, weight, and pediatric end-stage liver disease score), severe 25(OH)D(3)deficiency at presentation was independently associated with a higher risk of developing pulmonary infection in the early postoperative period (OR, 5.11, 95% CI, 1.30-20.16,P = .02). Conclusions 25(OH)D(3)deficiency is common and inversely correlated with pulmonary infection within the first month after pediatric LDLT. Our results indicate that preoperative serum 25(OH)D(3)deficiency is a potential biomarker for early pulmonary infection after pediatric LDLT.