A comprehensive quality survey for PCDDs/PCDFs in ambient air has been studied in Korea for two years. Monitoring was undertaken at two locations throughout Seoul (urban site) and Incheon (industrial site) in winter and spring. The periods are during 16 to 17 March 1998, 21 to 22 January 1999 and 28 to 29 April 1999 (Seoul) and 25 to 26 March 1998, 18 to 19 January 1999 and 26 to 27 April 1999 (Incheon). The values of PCDDs/PCDFs in ambient air were expressed as concentrations and international TEF values. The contents of PCDDs/PCDFs in urban site (Seoul) were lower than in industrial site (Incheon). The measurements in wintertime were higher than in springtime. The contents of 2,3,4,7,8-PeCDF with half toxicity of 2,3,7,8-TCDD were high. Thus we assumed to have an interest to the contents of 2,3,4,7,8-PeCDF. In this study, sample size was small (sample number was only 18) and sampling period was limited by 24 h. Therefore, we need more widespread and long-term surveys in order to estimate the human exposure by inhalation.