Gastroesophageal reflux disease (GERD) may make asthma difficult to control and may be a potential risk factor for frequent asthma exacerbations, but the mechanisms of the relationship between GERD and not well-controlled asthma remain unclear. The aim of this study was to explore the association of GERD with asthma control in adults. Patients with asthma were consecutively recruited, and Asthma Control Test (ACT) and Reflux Diagnostic Questionnaire scores were determined. The patients were categorized into not well-controlled asthma and well-controlled asthma groups according to the ACT score. Univariate and multivariate logistic regression analyses were performed to evaluate the relationship between GERD and not well-controlled asthma. Seven hundred and sixty-eight patients with asthma were enrolled. The mean ACT score was 18.2 ± 3.6, and there were 161 (21.0%) patients with not well-controlled asthma. The Reflux Diagnostic Questionnaire score was 10.5 ± 4.7, and 212 (27.6%) patients were complicated by GERD. Multivariate logistic regression analyses revealed the independent association of GERD with not well-controlled asthma (odds ratio, 3.12; 95% confidence interval, 1.53–4.88) after other established contributors to asthma control were adjusted. In conclusion, there is an association of GERD with not well-controlled asthma, independent of other potential contributors to asthma control.