Objective To investigate the relationship of body mass index with hiatal hernia （HH） and reflux esophagitis （RE）. Methods Two hundreds and twenty seven gastroesophageal reflux disease （CERD） patients with typical acid regurgitation and heartburn were enrolled and categorized into three groups according to body mass index （ BMI, kg,/m^2 ） as normal weight （ 18.5 ≤ BMI 〈 24）, overweight （24 ≤ BMI 〈 28 ）, and obesity （ BMI ≥ 28 ）. RE, non-erosive reflux disease （NERD） and HH were diag- nosed by gastroscopy. All the patients underwent ambulatory 24-hour pH monitoring and the pathological acid reflux was considered when the DeMeester seore≥ 15. Effects of BMI on RE and HH were estimated by using logistic regression analysis. Results The percentages of RE and HH were 30.0% （68/227） and 5.7% （13/227）, respectively. 76. 9% （10/13） HH patients had RE. Proportions of RE and HH increased significantly with increasing BMI （ P 〈 O. 05 ） , so was that of RE above grade B in three groups （ 6.4% , 16. 9%o and 31.6% ,P = 0. 003）. DeMeester scores of the three groups were 15.9, 19.8 and 36. 9, respectively （P 〈 0. 05 ）. The average 24hour intra-esophagus pH value of overweight group, was significantly lower than that of normal weight patients in the afternoon and midnight （ P 〈 O. O1 ）. Multivariate analysis showed obesity was a risk factor for HH with OR 7. 058 （95%o Cl： 1. 294 ～38.488, P = 0. 024） , male （ OR ： 2. 537, 95% CI： 1. 350～4. 766, P = 0. 004）, overweight （OR： 1. 921, 95% CI： 1. 005～ 3. 670, P=0.048） , obesity （OR： 3.305,95% CI. 1. 123 ～9.724, P=0.030） and HH （OR：6.879,95% CI. 1. 695～27. 913, P = 0. 007） were risk factors for RE. Conclusion BMI has a significant association with HH and RE, obesity is a common risk factor for both HH and RE, HH may induce the development of RE.