Objective To evaluate the effectiveness of noninvasive positive pressure ventilation(NPPV) as a weaning strategy in patients with acute respiratory failure after failure to wean from invasive positive pressure ventilation(IPPV). Method A prospective randomized and controlled clinical trial of weaning of IPPV was carried out in patients mechanically ventilated in mode of IPPV for more than 48 hours with failure in a spontaneous breathing trial(SBT: PSV 6 cmH_2O). Patients with contraindications to NPPV were excluded. After failure the SBT, patients were randomly divided(random number) in two groups. Patients in NPPV group were extubated after being ventilated with high pressure support for 30 minutes and then placed on NPPV. Patients in IPPV group were weaned following conventional procedure. Arterial blood gases, maximal inspiratory pressure, respiratory rate,tidal volume, rapid shallow breathing index, heart rate, arterial blood pressure, and peripheral oxygen saturation were measured before and after failing the SBT. The rate of complications, including pneumonia and tracheotomy duration mechanical ventilation, days of hospital stay and outcome were observed. Findings of the two groups were vompared using the Student t test and the chi-square test. Results The percentage of complications in the NPPV group was lower(22.9% versus 72.2%, P <0.01) ,with lower incidences of pneumonia(6.1%,36.1%; P <0.01) and tracheotomy. Compared between the two groups, days of ICU stay( 14.16(3.45) d vs. 22.57( 7.71 ) d; P <0.01) and total days of mechanical ventilation(14.88±3.76 days vs. 20.68± 2.79 days, P <0.01) of NPPV group are shorter than IPPV group. Conclusions NPPV is a good alternative to the mechanically venti-lated patients who fail in initial weaning attempts. The key to successful NPPV weaning is the proper selection of weaning candidates and using NPPV as soon as possible after extubation.