This study was performed to investigate the concentration of indoor aldehydes in children’s facilities. The samples were collected from various children\'s facilities (40 playrooms, 42 day-care centers, 44 kindergartens, and 42 indoor playgrounds) in summer (Jul~Sep, 2007), winter (Jan~Feb, 2008) and spring (Mar~Apr, 2008). The ratio of Indoor and outdoor (I/O) of aldehydes exceeds 1.0 and the formaldehyde levels in each child-care facilities were significantly different. We evaluated the lifetime cancer and non-cancer risk of young children due to indoor aldehyde exposure. We estimated the lifetime excess cancer risks (ECRs) of formaldehyde, acetaldehyde and the hazard quotients (HQs) of non-carcinogens (benzaldehyde and formaldehyde). Formaldehyde was evaluated for both carcinogenic and non-carcinogenic risk. The average ECRs of formaldehyde for young children were 1×10-4~1×10-5 level in all facilities. HQs of four non-carcinogens did not exceed 1.0 for all subjects in all facilities. Keywords：Aldehydes, Health risk assessment, Indoor air, Children\'s facilities