Abstract: Objective To study the association between gender and lung function in obese asthmatic children before and after inhaling corticosteroids (ICS). Methods A total of 102 asthmatic boys (including 57 normal-weight and 45 obese boys) and 88 asthmatic girls (including 46 normal-weight and 42 obese girls) received ICS treatment for one year. Pulmonary functions were evaluated before and after the treatment for forced expiratory volume in one second (FEV1), forced vital capacity (FVC), maximal expiratory flow 25 (MEF25) and maximal expiratory flow 50 (MEF50). Results The asthmatic children in the 4 subgroups showed similar pulmonary functions before the treatment. After inhalation of methacholine, FVC% and FEV1% were improved in both normal-weight boys and normal-weight girls; FVC% and FEV1% in obese boys were improved after the treatment, but the obese girls showed improvement only in FVC%. Conclusion Inhalation of methacholine can improve large airway function in asthmatic children, and gender affects the improvement to a lesser extent in normal-weight children. In obese asthmatic children, methacholine inhalation better improves lung functions in boys than in girls.