Abstract： Objective The study aims to investigate the clinical efficacy of combined N-acetylcysteine (Fluimucil) with Salmeterol/Fluticasone (Seretide,50/500 μg) in the treatment of chronic obstructive pulmonary disease (COPD).Methods Sixty cases of patients with stable COPD were selected and randomly divided into two equal sized groups,i.e.the treatment group and the control group.The patients in the treatment group were treated with a combined medication of N-acetylcysteine and Salmeterol/Fluticasone,while those in the control group only received Salmeterol/Fluticasone.At 3,6 and 12 months after medication,the values of FEV1 ％pred,PEF,6MWD,CAT and AECOPD were compared between the two groups.Results The values of FEV1 ％pred,PEF and 6MWD all depicted an ascending trend while that of CAT showed a descending one.From repeated-measures ANOVA on the pulmonary functions (FEV1 ％pred and PEF) in both groups,the differences between the two groups at each time intervals,the differences among the various time intervals and the group * time interactions were significant (P =0.000).The results of multiple analysis showed that the values obtained (FEV1 ％ pred and PEF) from the treatment group at 3,6 and 12 months were all higher than those from the control group correspondingly (P ＜0.05),and the values obtained from both groups at each of the time intervals post medication were all higher than those pre-treatment.For 6MWD and CAT,only the differences among the various time intervals and the group * time interactions were significant (P =0.000).The results of multiple analysis showed that 6MWD values obtained from the two groups at each time intervals all increased while CAT values at each time intervals all declined when compared with the pre-treatment findings.For the frequency of AECOPD,only the inter-group difference after implementing the treatments for consecutive 12 months were significant (x2 =4.44,P =0.035).Conclusions Besides improving the pulmonary function and the life quality for the patients with COPD,the combined treatment of N-acetylcysteine with Salmeterol/Fluticasone also proved to be efficacious in improving exercise tolerance and reducing the frequency of COPD exacerbations.