Background: The prevalence of allergic disease is increasing across the world. The development of allergic disease is associated with allergen sensitization. Objective: We investigated regional differences of allergen sensitization and relations between demographic characteristics and allergen sensitization among Jeongeup Countyside, Jeongeup City and Seoul City in Korea. Method: We conducted a cross-sectional survey of 1,792 children aged 9∼12 years from Jeongeup Countyside, Jeongeup City and Seoul City in Korea. A questionnaire and skin prick test for 16 common allergens were performed. Result: Participants from Jeongeup Countryside and City had more pets or livestock, siblings and breast feeding than those from Seoul City. A higher body mass index and a more frequent history of antibiotic therapy during infancy and parental allergy were found in Seoul City. The rate of sensitization to more than one allergens was higher in Seoul City than Jeongeup Countyside and City. The sensitization rate to cockroach was higher in Jeongeup Countyside and City than in Seoul City. The sensitization rate to Alternaria had a tendency to decrease with urbanization. The sensitization rate to house dust mite and cat were higher in Seoul City than in Jeongeup Countyside and City. Conclusion: The rate and type of allergen sensitization may differ among regions, which may be due to environmental or habitual factors. Therefore, allergen sensitization can be reduced by controlling these factors. (Korean J Asthma Allergy Clin Immunol 2010;30:277-284)