The objective of this study is to provide the research result of the actual condition about the concentrations of PM10, PM2.5, PM₁ and CO₂ in Seoul subway carriage. Mean concentrations of PM10, PM2.5 and PM₁, and CO₂ in subway carriage were investigated as 215.1 101.4㎍/m³, 86.9 38.6㎍/m³, 27.0 11.4㎍/m³, and 1,588 714ppm, respectively. These mean concentrations in subway carriages was higher when it ran on an underground track than on a ground track. For different hours, particulate matters concentrations were the highest in the morning, followed by noon and evening, and the CO₂ concentration was high in order of morning, evening and noon. In the result of the correlation among pollutants, as correlation between PM10 and PM2.5 was 0.92, and 0.94 between PM2.5 and PM₁. The inclusion rate of PM2.5 to PM10 was 41 7% and that of PM₁ to PM2.5 was 324%. In addition, CO₂ concentration had positive relation to the number of people, whereas the concentration of PM10 had negative correlation to the number of people. With these pollutants, the calculated result of adequate numbers of passengers in subway carriage by using regression equation showed 61 persons (34.06+0.04 CO₂(ppm) - 0.09 PM10(㎍/m³)(R²=0.30, p<0.01, n=707), which are needed to maintain each pollutant below the level of the criteria value, applicable to subway station.