Measurement of concentration and size distribution of TSP, ammonium, nitrate and sulfate were made from Mar., 1991. to June., 1992 in Seoul. The seasonal variation of concentration and size distribution of aerosols has been investiated. Aerosol were collected and size frationated by Andersen air sampler. Size classified samples were extrated with deionized water and analyzed for ammonium, nitrate and sulfate by ion chromatography. As the results of measurement, the average of concentration and MMAD(mass median aerodynamic diameter) were 118.58 ㎍/㎥, and 2.77 ㎛ for TSP, 1.92 ㎍/㎥ and 1.35 ㎛ for ammonium, 1.34 ㎍/㎥ and 1.58 ㎛ for nitrate, 8.52 ㎍/㎥ and 2.15 ㎛ for sulfate. The Seasonal variation of concentration and size distribution was observed for ammonium, nitrate and sulfate. The concentration peak of TSP was observed in coarse particles in spring and observed in fine particles in winter. The concentration`s distribution of TSP, ammonium, nitrate and sulfate was observed bimodal type during all season.