Pneumonia is a common illness affecting approximately 450 million people a year and occurring in all parts of the world (Ruuskanen et al., 2011). It is a major cause of death among all age groups resulting in 4 million deaths (7% of the world's total death) yearly (Kabra et al., 2010). The present study aimed to assess serum leptin in children with pneumonia and its relation to the clinical severity of the disease. The present study included 82 children aged 2months until 5 years of age presented with clinical picture of pneumonia. All children in the study were subjected to full medical history, thorough clinical examination and laboratory investigations including serum leptin for both ward and PICU and also chest X ray were done to all cases. Analysis of the results showed that:Serum leptin level was elevated in 35 pneumonic patients in both two studied groups the normal range (0 - 0.036 ng/mL) 29 patients (70.7%)of them were admitted in PICU and 6 patients(14.6%) in ward . Serum leptin was also correlated to the severity of the cases of the whole sample and was high in mild cases 8.6%, 37.1 % in moderate cases and 54.3 % in severe cases , but only significant correlation was with severe cases (19 patients) 54.3% who admitted in PICU (41 patients) and was diagnosed as severe according to signs and symptoms with (p value less than 0.001). About 44% of the ward patients(41 patients) were diagnosed as moderate cases and 17 % were as severe cases ,with significant correlation p value was 0.008 , and was in need for PICU admission. We found significant correlation with the increase in serum leptin in (19 patients who admitted in PICU) 65.5% with positive sputum cultures for Klebsiella organism with p value less than 0.001. we found that CRP level was higher in 39 PICU admitted patients (95.1%) with mean 120 mg|dl over 25 ward admitted patients (61%) with mean 14 mg|dl which was combined with high level of serum leptin, which indicates that serum leptin has a strong correlation with the severity of pneumonia as serum leptin was also high in severe cases with p value less than 0.001.