A large body of evidence suggests that long-acting β2-adrenoceptor agonist (LABA)/long-acting muscarinic antagonist (LAMA) combinations induce a strong synergistic bronchodilatory effect in human isolated airways. Moreover, a recent post hoc analysis demonstrated clinical synergism between LABAs and LAMAs, which induces a synergistic improvement not only in lung function but also in dyspnea in COPD patients.The aim of this study is to examine the baseline factors related to improvement in lung function or clinical symptoms that results from the administration of LAMA or LAMA/LABA and to compare the differences in improvement in lung function or clinical symptoms between LAMA and LAMA/LABA.Among 829 patients with COPD who were treated with LAMA or LAMA/LABA in our hospital, 112 patients (aged 40-89 years) matched the criteria. Of these 112 patients, 71 received LAMA (LAMA group) and 41 received LAMA/LABA (LAMA/LABA group) as the initial treatment. Various examination results such as lung function test values, symptom change, and frequency of exacerbations were compared between the two groups.Compared with the monotherapy, the combination therapy significantly improved the FEV1, inspiratory capacity (IC), and total COPD assessment test (CAT) scores. Comparing the improvement in each domain of the CAT produced by the combination therapy with that of the monotherapy, larger improvements were found for the domains of going out and sleeping. The frequency of exacerbations during the 24 weeks was significantly lower in the combination therapy group than in the LAMA monotherapy group (P=0.034). Although no relationship was found between improvement in FEV1 and any pretreatment factors in the LAMA/LABA group, the improvement in the CAT score was strongly related to the baseline CAT score, smoking index, and air trapping index (P-value <1×10-4).In this study of clinical practice, we found that LAMA/LABA combination therapy improved the clinical symptoms of COPD and IC and that the effects of the combination therapy were consistent with those observed in previous clinical trials.