During the period from April to September 2002, the size distributions of ambient aerosol were measured at the coastal site at Hamduk in Jeju Island. Na$^$+/, K$^$+/, Mg$^$2+/, Ca$^$2+/and Cl$^$-/ exhibited mostly a bimodal coarse mode size distribution, while ammonium and sulfate were mainly in the fine size range, with maximum at around 0.54$mu extrm{m}$. The average molar concentration ratio of ammonium to sulfate for fine particles was equal to 2.0${pm}$0.9. Nitrate was evenly found in both the coarse and fine modes. Elements like Al, Fe, Cu, Mg, Na, Ti, Sr and Mn were dominant in coarse particles, with the maximum at around 5.25$mu extrm{m}$. S and Pb were mainly in the submicrometer size range. Other elements with a fine and coarse modes were V, Ni, Cu, Ba and Mo. The patterns of the size distributions of trace elements measured at the downtown in Jeju City were very similar to those at the coastal site in Hamduk. However, the amplitude of size fractional concentrations at Jeju City was narrower than that at Hamduk. While the mass median diameters for the chemical species originated from the natural origin such as marine and crust were relatively large, those for ammonium, sulfate, S and Pb were very small.