BACKGROUND: In rural areas of China, the prevalence of obesity in children has grown continuously, becoming a major problem in the field of pediatrics. The purpose of this study is to investigate the relationship between Internet use and obesity in rural children and explore the mediating role of unhealthy dietary preferences. METHODS: This study empirically tested the impact of Internet use on obesity in rural children and its mechanism by using the survey data of Chinese rural primary and secondary school students, the OLS model, the two-stage least squares method, and the mediation effect model. RESULTS: This study provides new evidence that the prevalence of obesity is higher when more internet time is spent. When length of Internet use increased by one unit, the BMI-Z value of rural children increased by 11.2%. Analysis shows that Internet use has a significant impact on obesity through three types of unhealthy diets: "fast food preference", "snack food preference" and "soft drink and sugary fruit drink preference" (all at the 1% level). Heterogeneity analysis found that non-left behind (NLBC), male and depressed rural children's obesity was more significantly affected by Internet use (significant at 1%, 10% and 10%, respectively). CONCLUSIONS: This study provides new evidence that the prevalence rate of obesity is higher when more internet time is spent, especially in NLBC, boys and depressed children.