Objective To investigate the effects of different inspiratory rise time during noninvasive positive pressure ventilation ( NPPV) on work of breathing in patients with acute exacerbation of chronic obstructive pulmonary disease ( COPD) . Methods Eleven patients with acute exacerbation of COPD received different inspiratory rise time ( 0. 1sec, 0. 3sec, 0. 5sec) during NPPV. The changes of inspiratory muscle effort and breathing pattern of the patients were observed. Results The average respiratory rate,minute ventilation, and tidal volume were higher during NPPV compared with spontaneous breathing. But the changes of average minute ventilation and tidal volume were not significant ( P gt; 0. 05) . The pressure time product ( PTP) , transdiaphragmatic pressure ( Pdi) , and work of breathing of inspiratory muscle reduced significantly during different inspiratory rise time as compared with spontaneous breathing ( P lt;0. 01) . PTP,Pdi, and work of breathing reduced 59. 2% , 62. 7% , and 49% respectively when inspiratory rise time was 0. 1sec. They reduced more significantly during inspiratory rise time of 0. 1sec. Conclusions The present study confirms NPPV can unload inspiratory muscles in patients with acute exacerbation of COPD. It is more effective to reduce inspiratory load when inspiratory rise time is set at 0. 1sec while the patients feel most comfortable.