The trend of visibility variation of Seoul during 1980-1993 is analyzed. Annual average visibility has been decreased during the 1980s except 1988 and 1989 but not decreasing during the early 1990s. Also, the number of days with haze during 1983-1993 did not increase. Mixing height is deemed to be a dominant factor determining visibility. During the period, the difference between the average visibility at 6 p.m and 9 a.m decreased with the average visual range at 9 a.m slightly increased. Thus there is possibility that the effect of Photochemcial reactions becomes noticeable. The number of vehicles and the concentration of criteria air pollutants on the trend of visibility variation of Seoul would not be directly related to the variation of visibility.