Overlap syndrome of chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (OSA) leads to increased morbidity and mortality. There have been no reports available on the overlap syndrome for Koreans. Our primary aim was to identify prevalence and predictors of the overlap syndrome in Koreans.This is a cross-sectional study with a community-based sample of 1298 participants (mean age, 59.7 ± 6.7) from the cohort of Korean Genomic and Epidemiologic Study during 2013 to 2014. OSA and COPD were assessed by apnea-hypopnea index (AHI) and the ratio of forced expiratory volume in 1 s to forced vital capacity (FEV1/FVC < 70%), respectively, based on polysomnography and spirometry measurements. Using logistic regression with adjustment for the confounders identified by univariate analysis, odds ratio (OR) was estimated with 95% confidence interval (CI) of COPD among those with OSA.The prevalence rate of OSA was 45.8%, of which 32.8% were moderate-to-severe (AHI ≥ 15); 10.8% of those having OSA also had COPD, that is, the overlap syndrome. The prevalence of COPD remained the same as 10.8% regardless of the presence of OSA. The mean ratio of FEV1/FVC for those with COPD was 0.77, regardless of OSA. The OR increased for age (OR, 1.1; 95% CI, 1.0-1.1) and smokers (OR, 3.6; 95% CI, 2.0-6.4), but decreased for body mass index (BMI) (OR, 0.84; 95% CI, 0.8-0.9) and overweight state (OR, 0.4; 95% CI, 0.2-0.7). Risk factors of the overlap syndrome differed by OSA severity, that is, BMI in those with moderate-to-severe OSA, whereas sex (OR, 4.7; 95% CI, 2.1-10.6) and age (OR, 1.1; 95% CI, 1.0-1.1) in those with mild OSA.In a population study from Korea, 10.8% of OSA patients had an overlap syndrome with COPD. Although BMI is a well-known risk factor of OSA, it is likely that being overweight may be protective for moderate-to-severe OSA patients from the risk of COPD (i.e., overlap syndrome).