Seoul is one of the most dynamic capital cities in the world of which population is about 10.49 million. The air quality of Seoul subway is a great concern to users and the public authorities, especially the pollution of particulate matters. The metallic particulate matters are generated from the friction of wheels and subway rails, which causes dispersion into the platform and even to the trains. This study attempted to characterize the current filters in subway MVAC system and a newly developed filter which was a type of thin electret fiber bundle. Collection efficiency of the filtration system varies from 20% to 90% depending on filter life and dust particle size. The removal of fine dust with diameter smaller than 1㎛, which could not be well achieved by current filtration system, is very important in the subway air cleaning system. The new electret filter was found to have a high potential for the use in subway MVAC with high collection efficiency, especially for fine mode dust.