Objective To assess the effect of non-invasive positive pressure ventilation (NIPPV) in trea-ting acute exacerbation of chronic obstructive pulmonary disease (AECOPD) complicated with type Ⅱ respiratory failure. Methods Sixty-two AECOPD patients complicated with type Ⅱ respiratory failure was randomly divided into two groups: treated group of 30 patients and control group of 32 patients. The control group was treated with reg-ular medicine, the treated group were treated with NIPPV additional to regular medicine. The pH value, PaO_2, PaCO_2 and lactic acid level in blood gas were measured before and after treatment. Results The level of PH, PaO_2, PaCO_2 and lactic acid at 24 hours after treatment in the treated groups were 7.36 (SD:0.05), 84.0 (SD :8.9) ,57.0 (SD:7.9) and 1.63 (SD:1.15) respectively, which were significantly different to those of the control group (7.34 [SD:0.03] ,53.0[SD:12.4] ,62.0[SD:9.4] and 2.54[SD:1.28] ,respectively) (P <0.05). Conclusinons NIPPV is effective in treating patients with AECOPD and type Ⅱ respiratory failture.