Objective To evaluate the effects of inhaled bronchodilators on respiratory mechanics in moderate and severe chronic obstructive pulmonary disease（COPD） patients during eupnea.Methods Twenty moderate to severe COPD subjects were divided into three groups.Lung function，Borg score，breathing pattern and respiratory mechanics indexes were measured at baseline and 30 min after inhaled placebo，salbutamol 400 μg (or ipratropium 80 μg)，and ipratropium 80 μg (or salbutamol 400 μg) in sequence at interval as specified in different groups.Results In all groups，inhaled bronchodilators improved lung function (FEV1，FVC，IC) (Plt;0.05)，decreased Pdi，Peso，PTPdi，PTPeso and Raw (Plt;0.05，respectively)，in comparison with placebo.The reduction of PTPeso was positively correlated with the reduction of Peso (r=0.713，Plt;0.01）and Raw (r=0.602，Plt;0.01).Borg score decreased after inhaled bronchodilators (Plt;0.05).The reduction of dyspnea was positively correlated with the reduction of inspiratory work of breathing (ΔPTPeso%) (r=0.339，Plt;0.05) and Raw (ΔRaw) (r=0.358，Plt;0.05)，while was not associated with the changes of FEV1，FVC and IC.Conclusions In COPD patients，inhaled bronchodilators can reduce inspiratory work of breathing and airway resistance，the reduction of inspiratory work of breathing contributed to the reduction of airway resistance.Alleviation of dyspnea by inhaled bronchodilators is suggested to be ascribed to reduction of airway resistance and inspiratory work of breathing.