Background and Objectives: Constipation is a common complaint in children, which is not fatal but can affect quality of life. Several lifestyle-related risk factors for constipation have been reported, particularly dietary fac- tors, but results have been inconsistent. Here, we examined the relationship of dietary and lifestyle factors with constipation in Japanese preschool children using data of a nationwide study. Methods and Study Design: Sub- jects were 5,309 children aged 5 to 6 years at 380 nursery schools in 44 of 47 prefectures in Japan. Children hav- ing three or fewer bowel movements per week were considered constipated. Dietary intake data was collected us- ing a validated brief-type self-administered diet history questionnaire for Japanese preschool children, and infor- mation about general lifestyle was collected using a 4-page questionnaire designed for this study. Multivariate- adjusted odds ratios for constipation were calculated by logistic regression. Results: Higher dietary fiber intake was significantly associated with a lower prevalence of constipation (adjusted odds ratio: 0.62, p for trend: 0.005), but higher carbohydrate intake was marginally associated with a higher prevalence of constipation. Intake of po- tatoes, pulses, vegetables, and fruits intake decreased constipation prevalence, whereas higher rice intake was significantly and independently associated with higher prevalence of constipation. Regarding lifestyle factors, high physical activity and sufficient preparation time for breakfast and dinner for guardians were significantly as- sociated with lower prevalence. Prevalence tended to be negatively associated with a higher educational back- ground of the mother. Conclusions: Several lifestyle factors were associated with a lower prevalence of constipa- tion among Japanese preschool children, including dietary fiber intake.