The study on school indoor air quality was carried out at classrooms, computer-rooms, laboratories and play- grounds for carbonyl compounds including formaldehyde during the winter time from November to December 2004 and during the summer time from June to July 2005. The sampling was conducted under the general school condition without any artificial intervention such as the sealing, ventilating or heating at indoor environments. The concentrations of formaldehyde at all types of indoor environments were lower than air quality standard of $120{mu}g/m^3$ for public facilities. The mean concentrations of formaldehyde at indoors were $4.5{sim}6.1$ times higher than those at outdoors. From the comparison between two year and one year old schools after construction, the concentrations of formaldehyde in two year old school were $30{sim}38%$ lower than those in one year old school measured at classrooms and laboratories.