This study is aimed to estimate the PM_(2.5) source apportionment at Seoul intensive monitoring site located in Seoul metropolitan area. Time-resolved chemical compositions of PM_(2.5)are measured in real time using ambient ion monitor, semi-continuous carbon monitor, and on-line XRF at Seoul intensive monitoring site in 2010. The mass concentration of PM_(2.5) was simultaneously monitored with eight ionic species (SO42-, NO3-, Cl-, NH4+, Na+,K+, Mg2+, Ca2+), two carbonaceous species (OC and EC), and fourteen elements (Si, K, Ca, Ti, V, Cr, Mn, Fe, Co,Ni, Zn, As, Se, Pb) in 1-hr interval. The data sets were then analyzed using EPA PMF version 3 to identify sources and contributions to PM_(2.5) mass. EPA PMF modeling identified eight PM_(2.5) sources, including soil dust, secondary sulfate, secondary nitrate, motor vehicle, coal combustion, oil combustion, biomass burning, and municipal incineration. This study found that the average PM_(2.5) mass was apportioned to anthropogenic sources such as motor vehicle, fuel combustion, and biomass burning (61%) and secondary aerosols, including sulfate and nitrate (38%).