The mean frequency of sea fog occurrence in the west sea is higher than that in the east sea throughout the year and twice (5.3 days) the mean frequency in July than the east sea (2.5 days). The standard deviations of frequency are mostly as large as the mean frequencies because of large year to year variation. However, the order of sea in frequency is unchanged most years, as the frequency fluctuates simultaneously at all seas. Considering that both seas are located at the same latitude,this difference may result from different sea surface