During recent years, concerns over the effects of poor indoor air quality (IAQ) have been increased and wide spectrums of symptoms/illnesses are related to indoor air pollution in many urban centers of the world. In India, it is estimated that about half a million women and children die per year due to indoor air pollution. Therefore, maintaining an acceptable IAQ is important in places such as schools, corporate office buildings, hospitals and houses. It is hypothesized that the higher indoor pollutant concentrations of the buildings located near busy traffic roads are mostly influenced by elevated outdoor vehicular pollutant concentrations. In this paper an attempt has been made to analyze the indoor air quality of a naturally ventilated school building, Kendriya Vidyalaya, located in the Central Leather Research Institute (CLRI), Chennai, India. This building is located close to an urban road with heavy traffic flow, within a range of 100 m from the busy traffic junction. The indoor pollutants, namely carbon monoxide (CO) and carbon dioxide (CO2), along with meteorological parameters such as temperature and relative humidity, have been measured inside the school building. The vehicular pollutant CO has also been measured at the road side to develop the indoor and outdoor CO relationship. Further, a questionnaire survey has also been conducted to evaluate the general environmental conditions (sick building syndrome) of the school building. The result indicated that hourly the CO2 concentration inside the school room is 927 ppm during morning working hours (10.00a.m). This concentration is close to standard value of 1000 ppm specified by the National Institute for Occupational Safety and Health (NIOSH), USA. The measured CO concentrations inside the school building are well within the standard. During peak hour traffic flow on the adjacent road, a high level CO concentration has been observed inside the school building. The questionnaire survey at school shows that nearly 50% of students are suffering from minor health problems. © 2010 WIT Press.