Aim: The association between urbanization and childhood overweight/obesity (OWOB) in lower- and middle-income countries (LMICs) is poorly understood. Therefore, this study aimed to explore the association between residential district-level urbanization and OWOB among children under 5 years of age in Bangladesh. Subjects and methods: This study used data from a nationally representative sample of children under 5 years of age (N = 19,640) from the Bangladesh Multiple Indicator Cluster Survey 2012–13, including OWOB status of eligible children and other sociodemographic variables. District-level social and physical environmental features were used to create an urbanization index (low, medium, and high) using modified factor analysis. Individuals’ data were linked to the district-level urbanization index, and design-based binary logistic regression was used to explore the association between urbanization and OWOB. Results: Prevalence of childhood OWOB was 1.6%, and the average urbanization score was 37.4% (standard deviation: 8.7%). Childhood OWOB was higher in highly urbanized districts (2.0%) than in low urbanization districts (1.2%). The odds of OWOB was 53% higher in highly urbanized districts compared to low urbanization districts (adjusted odds ratio: 1.53; 95% CI: 1.01–2.31). Conclusions: Residential area urbanization was associated with childhood OWOB. These results suggest the importance of formulating context-specific prevention programs and policies to mitigate the adverse impacts of urbanization on childhood overnutrition in LMICs like Bangladesh. Future studies are required to understand its causal relationship with OWOB.