This study aimed to evaluate the variation in PM10 in the subways over the past years in Korea and to identify factors influencing the PM10 level. The PM10 measured internally by subway companies according to legal requirements was categorized by subway characteristics. These were statistically examined using a mixed effect model to identify the parameters influencing PM10 level. The PM10 levels monitored near platforms or waiting rooms ranged from 53.9 to 92.4 μg m-3 and were all below the 150 μg m-3 which is a regulatory standard. PM10 levels monitored on platforms were found to far exceed the yearly average atmospheric environmental standard (50 μg m-3). Based on both univariate and multiple analyses, several subway characteristics, including the presence of a platform screen doors (PSD), were found to be significantly associated with PM10 level, though there is little difference in significant factors among cities. Particularly, stations without transfer lines and the presence of PSD contributed to reduction in the PM10 level at the platform, except for Busan and in specific years.