Abstract： Objective To observe the clinical efficacy and therapeutic duration of oral corticosteroids in patients with acute exacerbations of chronic obstructive pulmonary diseases (AECOPD).Methods A randomized, double-blinded, placebo-controlled clinical study was designed. One hundred and thirty hospitalized patients with AECOPD were randomly divided into three groups: group 1 (n=44) received 30 mg/d of prednisone for 7 days and then placebo for another 7 days; group 2 (n=43) received 30 mg/d of prednisone for 10 days, then tappered to 15 mg/d for4 days; group 3 (n=43) received placebo for 14 days. The lung functions, arterial blood gas, length of stay, symptom scores, failure rate of treatment, side-effect of corticostetoids and the rate of relapse were evaluated before and after treatments.The results were analyzed by statistical package for social science (SPSS version 11.0), Measurement data were expressed by x±s, and t test was used for the comparison of the data before and after treatments. Chisquare test was used for the comparison of count data. Analysis of variance was applied to test for differences between the three groups. Multiple comparison was analyzed by SNK test. Fisher exact test was used for the comparision of the failure rate of treatment, the rate of relapse and safety evaluation. Results Compared with the placebo group [group 3, (0. 74±0. 32)L], the FEV1 in [group 1 (0.87±0.23) L and in group 2 (0. 93±0. 30) L]were significantly increased (F = 4. 53, P < 0. 05). The PaO2 in group 1 (79±9) mm Hg (1 mm Hg = 0. 133 kPa) and in group 2 (80±10) mm Hg were also increased significantly [group 3 was (73±12) mm Hg](F = 3.98, P < 0. 05). The length of stay (LOS) in group 1 (12. 5±3.5) d and in group 2 (12. 4±4. 1) d were shortened [group 3 was (13.5±3.6) d](F = 3. 82, P < 0. 05).However, no difference of FEV1, PaO2 and LOS was found between 7-day and 14-day durations of corticosteroids therapy. There were no differences in symptom scores, failure rate of treatment, side-effect of corticosteroids and the rate of relapse among the 3 groups. Conclusions Oral prednisone results in improvement of FEV1, PaO2 and LOS in hospitalized patients with AECOPD. A 7-day or 14-day duration of oral prednisone is of the same clinical efficacy. From these results, we recommend that 30 mg/d of prednisone for a 7-day duration is appropriate for the treatment of AECOPD.