Eighteen chronic obstructive pulmonary disease (COPD) cases (12 male, 6 female), age range 41-81 years, hospitalized with acute exacerbation but without respiratory failure nor indication of mechanical ventilation, were randomly enrolled in this study. Baseline spirometry and blood gas measurement results were recorded. After a 4-hour- BIPAP (bi-level positive airway pressure) treatment with an expiratory pressure (EPAP) of 5 cmH2O and inspiratory pressure (IPAP) of 15 cmH2O via nasal mask (BiPAP, Respironics, Inc, Murrysville, PA, USA) and, 4 hours after the end of this treatment spirometric tests and blood gase analysis were repeated. Four hours after BIPAP treatment most of the spirometric parameters improved (FEV1, p<0.01; FVC, p<0.01; FEV1/FVC, p<0.01). Although, there was no change in vital capacity (VC), the volume difference between VC and forced vital capacity was decreased at the 4th and 8th hours from baseline (respectively; p<0.01 and p<0.001). On the other hand, maximum voluntary ventilation values were significantly improved at the 4th and 8th hours after BIPAP treatment (respectively; p<0.001 and p<0.005). As to the other parameters related to the clinical aspects of COPD, subjective sense of dyspnea and ventilation scores per minute were lower at the 4th and 8th hours (respectively; p<0.001, p<0.001 and p<0.001, p<0.001). Pulse rates were also lower soon after BIPAP and at the 8th hour (respectively; p<0.001, and p<0.01). Consequently, we suggest that BIPAP treatment may have a beneficial effect on pulmonary functions and clinical symptoms in COPD patients without acute respiratory failure or indication of mechanical ventilation.