Background: In clinical practice, some patients with asthma show incompletely reversible airflow obstruction, resembling COPD. This overlap phenotype is not yet well defined in asthma patients. Methods: A total of 566 patients with a diagnosis of asthma based on either 1) physicians diagnosis with at least 6 months history of inhaler use, 2) positive response to bronchodilator: ＞200 ml FEV1 and ＞12% baseline, or 3) positive methacholine or mannitol provocation test, were enrolled. We evaluated their clinical features, serum eosinophil counts, serum total IgE with allergy skin prick test, spirometry, methacholine or mannitol provocation challenges and bronchodilator responses based on their retrospective medical record data. Results: The study population was subdivided into two groups according to their presence of airflow obstruction: asthma (40%, n=224, postbronchodilator FEV1/FVC≥70) and the overlap group (60%, n=342, postbronchodilator FEV1/FVC ＜70). The overlap group had a higher lifetime smoking intensity (29 vs 20.8 pack years, p=0.016) and a lower BMI (23.8 vs 24.9kg/m2, p=0.000) than the asthma group. The overlap group showed a lower postbronchodilator FEV1 (74.9 vs 95.7%, p=0.000), more positive results of airway hyperresponsiveness either with methacholine or mannitol (67 vs 21%, p=0.000) and bronchodilator response (87 vs 28%, p=0.000) compared to the asthma group. Conclusions: The overlap group was significantly associated with a lower FEV1, lower BMI, a more positive bronchodilator response and AHR.