Pneumonia is a common respiratory infectious disease in infancy. Previous work shows controversial results on the benefit of zinc supplementation in patients with pneumonia. We conducted this study to investigate serum zinc status amongst infants with severe pneumonia and the clinical impact that zinc supplementation has on those patients with low serum zinc levels. This study design was a non-blinded prospective randomized controlled trial. The study is approved by the Ethics Committees of Beijing Children's Hospital. A total of 96 infants diagnosed with severe pneumonia and hospitalized in the pediatric intensive care unit between November 2011 and January 2012 were enrolled. Enrolled patients were divided into low serum zinc and normal serum zinc group. The low serum zinc group was randomized into treatment and control groups. Only the treatment group received zinc supplementation within 48-72 hours after hospitalization. The prevalence of zinc deficiency on admission was 76.0%. The low zinc level was most apparent in infants between 1 and 3 months of age. The serum zinc level increased in the zinc treatment group and returned to a normal level (median, 53.20 mu mol/L) on day 12 +/- 2. There was no statistical difference in the pediatric critic illness score, lung injury score, length of hospital stay, and duration of mechanical ventilation between the zinc treatment group and control group. Zinc deficiency is common in infants with severe pneumonia. Normalization of zinc levels with zinc supplementation did not improve clinical outcomes of infants with pneumonia.