The association between gastroesophageal reflux disease (GERD) and asthma is well accepted. The prevalence of GERD increases in asthmatics compared with normal controls, whereas GERD may induce or exacerbate asthma. They interact with each other in a cause and effect relationship. But the mechanism by which GERD might induce or aggravate asthmatic symptoms remains unclear. Two mechanisms have been proposed, including (1) acid in the inflamed esophagus acting on exposed receptor causes an increase in bronchial hyper-responsiveness via the vagal reflex; (2) microaspiration of gastric contents damage the bronchial mucosa, which result in inflammation of the mucosa and bronchial hyper-responsiveness. Among the GERD diagnostic methods, ambulatory esophageal pH monitoring bears the highest sensitivity. Ambulatory esophageal pH monitoring is recommended in patients without classic reflux symptoms or those with difficult to control asthma. Both medical and surgical antireflux therapy could improve asthma symptoms, asthma medication requirements, and even pulmonary function in a proportion of asthmatics.