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 $0.3~25{mu}m.$. The obtained results were compared with $PM_{2.5};and;PM_{10}$ data during Asian dust events. The results show that the size resolved aerosol number concentration from OPC measurement has a similar tendency with $PM_{10};and;PM_{2.5}$ mass concentration. During Asian dust periods, the number concentrations in large particle $(CH5~CH8)$ increase more than small particles which diameter is less than $2.23{mu}m(CH5)$ and the same results were shown when $PM_{10}$ was compared with $PM_{2.5}$ 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.