Background: Recurrent aphthous stomatitis (RAS), a common oral mucosal disorder characterized by chronic, inflammatory, and ovoid ulcers, has a complex aetiology. The purpose of the study was to investigate the dietary factors influencing the prevalence of RAS.Methods: A total of 754 participants aged 18 to 59 years in Nanjing were enrolled in this descriptive cross-sectional study. An anonymous questionnaire was adopted to investigate the distribution of RAS, dietary factors, self-reported trigger factors and therapeutic methods.Results: Among all participants, the prevalence rate of RAS was 21.4%. Univariable analysis identified fruits, dairy products, vegetables and drinking water, but not fried foods, fermented foods, spicy foods, or eggs, as influencing factors of RAS. After adjusting for age and sex, multivariable regression analysis identified fruits (adjusted odds ratio [aOR] = .432, 95% confidence interval [CI] = [.219-.853], p = .015) and drinking water (aOR = 3.603, 95% CI = [1.280-10.147], p = .015) as protective factors of RAS. Conclusion: RAS is prevalent among the 18- to 59-year-old Nanjing population. A lower intake of fruits and drinking water might be associated with a higher prevalence of RAS. These factors could be used as daily preventive measures for RAS.