Exercise-induced bronchoconstriction (EIB) in asthmatic children has been associated with obesity. Leptin, the proinflammatory adipokine, is typically increased in obesity, whereas cysteinyl leukotrienes (cysLTs) are the main inflammatory mediators implicated in the pathogenesis of EIB. The aim of this work was to study the possible impact of obesity on the severity of EIB in asthmatic children and the possible association with the adipokine leptin.  The study included eighty pre-pubertal asthmatic children divided according to their body mass index (BMI) and response to exercise into four groups; obese exercise-responders (n=20), normal-weight exercise-responders (n=20), obese exercise non-responders (n=20), and normal-weight exercise non-responders (n=20). A baseline spirometry test and a standardized exercise challenge test (ECT) were performed. The severity of EIB was assessed by the maximum percentage fall in forced expiratory volume in 1 second (MF%FEV₁) after exercise. The level of fasting serum leptin and the release of cysLTs during exercise were compared between the 4 groups. The MF%FEV₁ during exercise was significantly greater in obese responder compared to normal-weight responder patients (p=0.004) and MF%FEV₁ was positively correlated with cysLT release during exercise, BMI z-score, waist circumference and serum leptin. CysLT release during exercise was positively correlated with the level of serum leptin (r =0.514, p=0.001). This study reports that the severity of EIB is significantly greater in obese compared to normal-weight asthmatic children and suggests an association between leptin and airway hyperresponsiveness to exercise in obese asthmatic children through a mechanism related to cysLT release