Objective: To describe the status quo of overweight and obesity among children aged 3 to 5 in Beijing and Tokyo, and to explore its relationship with lifestyle. Methods: Using the method of cluster stratified random sampling, a sample of 444 children aged 3-5 years from Beijing and Tokyo were selected in Oct. and Nov. of 2019. Height, weight and lifestyle were measured. Overweight and obesity among children in the two cities and its relationship with lifestyle were compared and analyzed. Results: Average level of BMI, rate of overweight and obesity of children in Beijing(25.28%) were higher than those in Tokyo( 18.44 %). There were significant differences in overweight and obesity rates between children in Beijing and Tokyo with physical activity before breakfast( χ 2=29.14, 31.18, P <0.05). There were significant differences in overweight and obesity rates between children in Beijing and Tokyo with different snack frequency after dinner( χ 2=24.72, 21.93, P <0.05). Logistic regression analysis further showed that children s lack of physical activity before breakfast in Beijing is positively related to overweight and obesity( OR= 1.45, 95%CI =1.10-2.68). Beijing children who often eat snacks after supper ( OR=2.56, 95%CI =1.44-3.57,) and sometimes eat snacks were positively correlated with the occurrence of overweight or obesity ( OR=1.72, 95%CI =1.21-2.72). Conclusion The prevalence of overweight and obesity among preschool children in Beijing is higher than that in Tokyo. Potential risk factors for overweight and obesity among infants in Beijing include lack of physical activity before breakfast and frequent snacking after dinner.