Continuous measurements of the extinction coefficient( $b_{ext}$ ) and scattering coefficient due to Particle( $b_{sp}$ ) were made during the fall 1993 in Seoul along with the measurements of the size distribution, ionic composition of particles. On the average, $b_{sp}$ values are 55% and 79% of $b_{ext}$ values during the clear and smoggy Periods respectively. Also the average values of $b_{ext}$ and $b_{sp}$ were 0.791$ imes$10$^{-3}$ $m^{-1}$ (visual range 4.9km) and 0.628$ imes$10$^{-3}$ $m^{-1}$ (visual range 6.2km) during the smoggy Period, and 0.297$ imes$10$^{-3}$ $m^{-1}$ (visual range 13.1km) and 0.164$ imes$10$^{-3}$ $m^{-1}$ (visual range 23.8km) during the clear period, respectively. The Peak at about 1${mu}{ extrm}{m}$ of the Particle size distribution during the smoggy period is about four times higher than that during the clear period while the peaks at about 5${mu}{ extrm}{m}$ during both periods are similar. Also, the concentrations of sulfate and nitrate at about 1${mu}{ extrm}{m}$ during the smoggy Period are much higher than these during the clear Period.eriod.