In this study, the size-fractionated aerosols were collected using a 8-stage cascade impactor at Gosan Site of Jeju Island in spring seasons of 2010-2011, and their chemical compositions were analyzed in order to understand the pollution characteristics, especially for the acidification and neutralization properties. The mean concentrations of ionic components during Non-Asian Dust events were in the order of nss-SO42- > NO3- > HCO3- > Na+ > NH4+ > Cl- > nss-Ca2+ > K+ > Mg2+ > H+ and those of elemental components were in the order of S > Ca > Na > Al > K > Mg > Fe > Zn > Ba > Sr > Ti > Pb > Cr > Ni > Mn > Cu > Mo > V > Cd > Co. The size distributions of NH4+, nss-SO42- and S which are mainly originated from anthropogenic pollution sources were mostly in the ultrafine particle mode (0.4∼1.1 μm) and showed a bi-modal pattern. On the other hand, the size distributions of NO3-, nss-Ca2+, Na+, Cl-, Al, Na, Ca and Fe which are, except NO3-, mostly influenced by soil and marine sources were mainly in the coarse particle mode (>3.3 μm) and showed a mono-modal pattern. Consequently, the anthropogenic components (NH4+, nss-SO42-, S, Zn, Pb) were distributed as in the order of ultrafine > fine > coarse particles, but the natural components (Na+, Cl-, Mg2+, nss-Ca2+, Al, Na, Ca, Fe, Mg) and NO3- were as in the order of coarse > fine > ultrafine particles. H2SO4 and HNO3 were the main contributing compounds on the acidification of atmospheric aerosol in Jeju area, whereas NH3 and CaCO3 contributed to their neutralization. The neutralization by NH3 in ultrafine, fine, and coarse particles was 78, 44 and 28%, and that by CaCO3 was 7, 36, 62%, respectively. The measurement of number concentrations of atmospheric aerosols for Asian Dust and Non-Asian Dust periods has resulted that the overall increases of number concentrations over 0.30 μm are identified during Asian Dust events, especially 15.9 times higher at the range of 30.0～32.0 μm compared to those for Non-Asian Dust periods.