A visibility analysis model based on the Mie theory is applied to the measurements during the fall, 1993 in Seoul. Model estimations of the total extinction coefficient $b_{ext}$, and the particle scattering coefficient, $b_{sp}$ are in good agreement with the measured values by a transmissometer and a nephelometer, respectively. These values show strong dependency on the mass loading of fine particles( $D_{p}$ ＜3.0${mu}{ extrm}{m}$) but show no apparent relation with that of coarse particles(3.0${mu}{ extrm}{m}$＜ $D^{p}$ ＜10${mu}{ extrm}{m}$). Relative humidity plays an important role in determining the size of particles which in turn, affects the optical efficiency of aerosol. Based on the composition analysis with cut size nitrate concentration is higher than the sulfate concentration in PM3-10 but they are comparable to each other in PM3. Considering in 1985, it demonstrates a drastic increase of nitrate concentration between 1985 and 1993. It is found that measured and estimated light extinction budget were in good agreement within 10% and that scattering by particles is responsible for about 50-55% and 70-80 % of total extinction during clear and smoggy periods respectively.y.