The purpose of this study was to investigate air quality in Chungju, Korea, using data obtained with local air quality monitoring system. We had cohort studies to investigate the relations between environmental pollution and health of residents near large industrial complexes since 2004. This study analyzes the O₃, NO₂, SO₂, CO and PM10 concentration in Chungju from 2002 to 2006. Air pollutant is closely related to number of manufacturing facilities and cars, energy utilization and weather conditions. Generally, the diurnal concentration of air pollutants in Chungju reached the highest level in the morning (about 08:00~) and early evening (about 19:00~). On the other hand, the diurnal concentration of ozone recorded the highest amount in late afternoon (about 16:00~) and lowest in early morning (about 08:00~). Air pollutants concentration of Chungju was highest from winter to spring and lowest during summer season. On the other hand, monthly variation of ozone concentration was greatest in June and smallest in December. Besides, PM10 concentration posted the highest record in April and the lowest during September. Generally, this study analyzed air pollution changes in Chungju as well as in large scale industrial complex regions such as Ulsan, Pohang, Kwangyang, Sihwa Panwol and Gangneung in Korea. We compared the air quality of Chungju with those of these cites and found that air pollutants except for CO in Chungju was generally lower than large industrial complex regions.