To determine the effect of air pollutants in Taejon City, we used medical insurance claim data for asthma and the data monitored from telemetry system of Ministry of Environment for air pollutants and meteorological factors. From November 1st, 1997 to October 31th, 1998, 95,629 asthma patients were covered by medical insurance at Taejon City. Subjects were composed of 49,563 males (51.8%) and 46.336 females(48.2%), and among the subjects, the proportion under 15 years old was 62.8% of the total. During the study period, daily mean concentrations of each air pollutants-So2, No2, CO, O3 and TSP-were 9.8 ppb, 17.6 ppm, 1.414 pp, 17.3 ppb and 60.6 $\mu\textrm{g}$/㎥, respectively, which were lower than each of the environmental recommended exposure levels, Through the simple correlation analysis between each air pollutants and meteorological factors, O3 was positively correlated with temperature, but negatively with relative humidity. TSP, SO2, NO2, CO were negatively correlated with meteorological factors, and these air pollutants except O3 were positively correlated with each other, O3 was correlated with TSP positively but the others negatively. Estimating relative risks of each air pollutant with the baseline general additive model, daily mean concentrations of TSP(Lag 0, 1, 4, 5day) were significantly associated with the increase of the asthma admission. Two age subgroups, under 15 and 15~54 have shown various association of all air pollutants concentration with the asthma admission. However, in case of over 54 age subgroup, only TSP(Lag 0 day) among all air pollutants was associated with the asthma admission. Each of ambient outdoor pollutant concentrations in Taejon City are significantly associated with the admission of asthma patients even though all concentrations in Taejon City are significantly associated with the admission of asthma patients even though all concentrations were much lower than the environmental recommended exposure levels. Therefore, continuous effort lowering air pollutant concentration and introducing an active environmental conservation policy should be implanted for preventing hazardous health effects. Considering major proportion of asthma admissions, high susceptibility and less confounding factors among the age subgroup under 15 will be a useful target population for assessing such health effect monitoring.