Background Patients with bronchiectasis are often treated with bronchodilators such as long-acting muscarinic antagonists (LAMA) or long-acting beta-agonists (LABA) for their symptoms, but empirical evidence supporting such practice is sparse. We evaluated the effect of LAMA and LABA on lung function improvement in patients with bronchiectasis. Methods Using the in-house patient database at a tertiary referral hospital in Seoul, South Korea, we extracted data from patients diagnosed as bronchiectasis with computed tomography (CT) scan and treated with LAMA, LABA, or both. Patients with asthma, chronic obstructive pulmonary disease (COPD) or a history of cigarette smoking were excluded, and a subgroup analysis was performed in patients who did not receive concurrent treatments such as antibiotics, mucolytics or systemic steroids that may affect lung function improvement. Results A total of 230 patients (males: 32.6%, median age: 60 years) were analyzed. Their mean forced expiratory volume in 1 second (FEV1) was 53.3% of the predicted value [standard deviation (SD), 15.3]. The patients received LAMA (n=95), LABA (n=36), or both (LAMA-LABA; n=99), after which their FEV1 values were increased by 0.102 liters (SD, 0.208; P<0.001), 0.133 liters (SD, 0.181; P<0.001), and 0.122 liters (SD, 0.230; P<0.001), respectively. In a subgroup of 97 patients who did not receive concurrent treatments, the FEV1 was increased by with 0.107 liters (SD, 0.167; P<0.001), 0.165 liters (SD, 0.209; P=0.005), and 0.165 liters (SD, 0.187; P<0.001) in the LAMA, LABA, and LAMA-LABA groups, respectively. Baseline FEV1 had a significant negative correlation with response to bronchodilator treatment in the total patient cohort (R=−0.242, P<0.001) and the subgroup of patients without concurrent treatments (R=−0.386, P<0.001). Conclusions Treatment with bronchodilators such as LAMA or LABA was effective in improving lung function in patients with bronchiectasis, regardless of concurrent treatments that also improve lung function. These data may support the use of LAMA and LABA in patients with bronchiectasis.