To investigate the chemical characteristics of PM2.5 in Seoul, Korea, atmospheric particulate matters were collected using a PM10 dichotomous sampler including PM10 and PM2.5 inlet during the period of October 2000 to September 2001. The Inductively Coupled Plasma-Mass Spectromety (ICP-MS), Ion Chromatography (IC) methods were used to determine the concentration of both metal and ionic species. A statistical analysis was performed for the heavy metals data set using a principal component analysis (PCA) to derived important factors inherent in the interactions among the variables. The mean concentrations of ambient PM2.5 and PM10 were 24.47 and 45.27 ㎍/㎥, respectively. PM2.5 masses also showed temporal variations both yearly and seasonally. The ratios of PM2.5/PM10 was 0.54, which similar to the value of 0.60 in North America. Soil-related chemical components (such as Al, Ca, Fe, Si, and Mn) were abundant in PM10, while anthropogenic components (such as As, Cd, Cr, V, Zn and Pb) were abundant in PM2.5. Total water soluble ions constituted 30～50 % of PM2.5 mass, and sulfate, nitrate and ammonium were main components in water soluble ions. Reactive forms of NH4+ were considered as NH4NO3 and (NH4)2SO4 during the sampling periods. In the results of PCA for PM2.5, we identified three principal components. Major contribution to PM2.5 seemed to be soil, oil combustion, unidentified source. Further study, the detailed interpretation of these data will need efforts in order to identify emission sources.