This study investigated the indoor air concentrations and the harmful effects on health by hazardous pollutants in the normal classrooms and special classrooms of 132 elementary, middle, and high schools located in 13 sites in Chungnam from February 2006 to June 2007. The results obtained from this investigation are as follows. As the results of the survey on the indoor air quality, volatile organic compounds were higher in normal classrooms(251.67㎍/㎥) than special classrooms (181.59㎍/㎥), and formaldehyde was significantly higher in special classrooms (34.22㎍/㎥) than normal classrooms (24.61㎍/㎥). With regards to the differences of pollutant distribution among elementary, middle, and high schools, volatile organic compounds were the highest in elementary schools (210.79㎍/㎥) followed by middle schools (207.79㎍/㎥) and high schools (195.96㎍/㎥), and formaldehyde was the highest in high schools (36.03㎍/㎥) followed by elementary schools (29.84㎍/㎥) and middle schools (29.16㎍/㎥). With regards to the mean concentration of pollutants by school building age, VOCs were the highest in less than 1 year old classrooms (410.93㎍/㎥), followed by less than 3 years old classrooms (156.52㎍/㎥) and less than 2 years old classrooms (120.18㎍/㎥). Formaldehyde was also investigated to be significantly higher in less than 1 year old classrooms (41.37㎍/㎥) than 2 or 3 years old classrooms (31.50㎍/㎥, 22.21㎍/㎥, respectively). Keywords：Indoor air, School, Volatile organic compounds, Formaldehyde