This real-world study evaluated the efficacy of once-daily long-acting β2-agonist (LABA)/long-acting muscarinic antagonist (LAMA) fixed-dose combinations (FDCs) for improving lung function in patients with chronic obstructive pulmonary disease (COPD). Patients with COPD who were treated with once-daily LABA/LAMA FDCs for 12 months were included. We evaluated their lung function improvement after 12 months of treatment with different LABA/LAMA FDCs. A total of 198 patients with COPD who were treated with once-daily LABA/LAMA FDCs were analyzed. A total of 114 patients were treated with umeclidinium/vilanterol (UMEC/VIL); 34 patients were treated with indacaterol/glycopyrronium (IND/GLY); and 50 patients were treated with tiotropium/olodaterol (TIO/OLO). The forced expiratory volume in 1 s (FEV1) was significantly increased in the patients treated with all three once-daily FDCs (55.2% to 60.9%, p = 0.012 for UMEC/VIL, 58.2% to 63.6%, p = 0.023 for IND/GLY, and 54.1% to 57.7%, p = 0.009 for TIO/OLO). The treatment of COPD patients with TIO/OLO resulted in a significant improvement in both forced vital capacity (FVC%) (71.7% to 77.9%, p = 0.009) and residual volume (RV%) (180.1% to 152.5%, p < 0.01) compared with those treated with UMEC/VIL (FVC%: 75.1% to 81.5%, p < 0.001; RV%:173.8% to 165.2%, p = 0.231) or IND/GLY (FVC%: 73.9% to 79.3%, p = 0.08; RV%:176.8% to 168.3%, p = 0.589). Patients treated with UMEC/VIL or TIO/OLO showed significant improvement in FVC. In addition, those receiving TIO/OLO also showed significant improvement in RV reduction.