Background While the clinical characteristics and outcomes of asthma‐chronic obstructive pulmonary disease (COPD) overlap (ACO) have been frequently compared with those of COPD or asthma, the prevalence and features of ACO in patients with severe asthma are unclear. Objectives Evaluation of the prevalence and clinical features of ACO using the Korean severe asthma registry. Methods At the time of registration, ACO was determined in patients with severe asthma by attending specialists. Patients were classified into ACO and non‐ACO groups, and the demographic and clinical characteristics of these two groups were compared. Results Of 482 patients with severe asthma, 23.7% had ACO. Patients in the ACO group were more likely to be male (P < .001), older (P < .001), and ex‐ or current smokers (P < .001) compared with those in the non‐ACO group. Patients in the ACO group had lower mean forced expiratory volume in 1 second (P < .001) and blood eosinophil percentage (P = .006), but higher blood neutrophil percentage (P = .027) than those in the non‐ACO group. The ACO group used more inhaled long‐acting muscarinic antagonist (P < .001), methylxanthine (P = .001), or sustained systemic corticosteroid (P = .002). In addition, unscheduled emergency department visits due to exacerbation were more frequent in the ACO group (P = .006). Conclusion Among patients with severe asthma, those with ACO were older, predominantly male, and were more likely to have a smoking history than those with asthma only. Patients with ACO used more systemic corticosteroid and had more frequent exacerbations related to emergency department visits than those with severe asthma only. We found that about one‐fourth of patients with severe asthma was diagnosed with ACO by specialists. The most common reason for ACO diagnosis was smoking history. ACO patients were predominantly male, older, and had more smoking history compared with non‐ACO patients. ACO patients had higher blood neutrophil count, but lower lung function. ACO patients used more LAMA, methylxanthine, and systemic corticosteroid and had more frequent exacerbations related to ER visits compared with those with severe asthma only. Abbreviations: ACO, asthma‐COPD overlap; ER, emergency room; FEV1, forced expiratory volume in one second.