The purposes of this study were to characterize indoor air concentration, to see the correlation of each parameter, to recognize main contribution factor of indoor air pollutants and to suggest that IAQ management plan should be established through investigation of IAQ status in the subway stations and carriages. Afield study was designed to characterize indoor concentrations and sources in subway stations in Seoul metropolitan area, Korea during June to December, 2005. This characterization was carried out in two steps: the first step of this survey was to determine the distributions of indoor measurements of ten pollutants in all of 34 subway stations, whereas the second step of survey was to determine the temporal variation of'PM10 concentration during the subway carriages operating hour between 07:00 to 20:00. Sampling point of subway stations was concourse and platform. The mean concentrations of PM10 and CO 2 were 119.82 μg/m3, 674.94ppm, respectively. About 11.8% of both platform and concourse of the mean CO2 concentration in 34 stantions were above lOOOppm of the Korea Standard of IAQ. The mean concentration of volatile organic compounds(VOC) and total suspended bacteria(TBC) were 717.17 μg/m3, 533.42 CFU/m3respectively. To survey was to determine the temporal variation of PM10 concentration in subway carriages. Results of ANOVA-analysis indicated that PM10 concentration between 7:00 to 9:00 was significantly higher than that 11:00 to 13:00 and 18:00 to 20:00(p<0.05).