Exposure to indoor air pollutants in closed microenvironment such as underground subway spaces is a serious health concern. The underground subway system is confined space consists of limited ventilation, compact design, high population density, variety of air pollution sources and environmental conditions. The key air pollutants that can accumulate in subway microenvironment are particulate matter (PM), carbon monoxide (CO), volatile organic compounds (VOCs), ozone (O3), bioaerosols and oxides of nitrogen (NOx). In the past, several studies were focused on characterization of PM in underground subway platforms and trains and few studies were also focused on characterization of gaseous and biological pollutants. Most of these studies concluded that air pollutant concentrations inside subway station are significantly contributed by the outdoor air pollution source i.e. vehicular exhaust emissions. These studies are also indicated that increased passenger density in subway microenvironment can causes high levels of carbon dioxide and bacterial concentrations. In this seminar the preliminary results of air pollutants and human comfort parameters monitored in underground subway stations in Chennai city, India will be discussed.