The characteristics for the aerosol number distribution was studied during spring, 2004 in Incheon. Optical Particle Counter (OPC, HIAC/ROYCO 5230) was used in order to measure the number concentration of aerosol in the range of 0.3～25㎛. The obtained results were compared with PM2.5 and PM10 data during Asian dust events. The results show that the size resolved aerosol number concentration from OPC measurement has a similar tendency with PM10 and PM2.5 mass concentration. During Asian dust periods, the number concentrations in large particle (CH5～CH8) increase more than small particles which diameter is less than 2.23㎛(CH5) and the same results were shown when PM10 was compared with PM2.5 data compared with non-dust days, Consequently, this study shows that size resolved aerosol number concentration from OPC measurement can be used as a useful tool in comparison of mass concentration data.