Objective To analyze the relationship between small intestinal bacterial overgrowth (SIBO) and gastroesophageal reflux disease (GERD). Method A total of 5832 patients who visited the Department of Gastroenterology, the Sixth Medical Center of Chinese PLA General Hospital from August 2019 to August 2021 were selected. The patients were divided into GERD group (n=1752) and non-GERD group (n=4080) according to gastroesophageal reflux disease. The two groups were compared for general features and SIBO prevalence. Subgroup analysis was performed in GERD group. The gastroesophageal reflux disease questionnaire (GerdQ) scores between the SIBO-positive group (n=1051) and the SIBO-negative group (n=701) were compared. The prevalence of SIBO was compared between the group with proton pump inhibitor (PPI) (n=1280) and the group without PPI (n=472). The prevalence of SIBO was compared between patients in non-erosive esophagitis (n=1051), erosive esophagitis (n=643) and Barrett's esophagus (n=58). Risk factors for GERD were analyzed by multivariate logistic regression. Results Age, body mass index, GerdQ score, smoking and prevalence of SIBO in GERD group were higher than those in non-GERD group (P<0.05). Multivariate analysis found that SIBO, obesity, drinking and smoking were risk factors for GERD. Subgroup analysis showed that the GerdQ score in SIBO-positive group (9.54±1.59) was higher than that in SIBO-negative group (8.40±1.54, P<0.05). The prevalence of SIBO in patients taking PPI (64.9%) was higher than that in patients without PPI (46.6%, P<0.05); The prevalence of SIBO in patients with erosive esophagitis (68.7%) and Barrett's esophagus (69.0%) was higher than that in patients with non-erosive esophagitis (54.1%, P<0.05). Conclusions SIBO is risk factor for GERD. Reflux symptoms are more severe when GERD patients have SIBO.