Metro is considered the most popular method of passenger transportation in many metropolises of the world due to its high capacity of passenger transportation and good safety. So far, many studies have been conducted on particulate matter pollution in closed environments, but few studies have been conducted to measure air pollution in Tehran metro. In this study, the concentration of particulate matter less than 2.5 μg/m3 in diameter) PM2.5(was measured in the main metro line of Tehran in winter. For a sampling of suspended particles, a portable direct reading device for suspended particles (HAZDUST EPMA5000) was used. To analyze the data, the Analysis of variance) ANOVA (test was used to compare the particle concentrations in different locations of the station and a T-test was used to compare the PM2.5 particle concentrations in the ground level and underground Metro stations. the concentration of PM2.5 particles in the platforms, ticket halls, and outside the stations was significantly different (P <0.001). There was a significant difference between the concentration of PM2.5 particles in the stations and the daily ticket hall with the underground (P <0.018). the average concentration of airborne particles PM2.5 at the stations was 45 μg/m3 that more than the Standard limit and the average concentration of PM2.5 particles on platforms and ticket sales halls in underground stations is more than on the ground stations.According to the research results, the use of warm ventilation system in winter with a suitable filter is recommended.