The seasonal data obtained at National Fisheries Research and Development Institute from 1989 to 1994 were analyzed to investigate the seasonal variations of temperature and salinity in incheon coastal area. In the tidal flats covering from Incheon harbor to Sorae, the mean temperatures are higher, the amplitudes of flats, the mean salinities are lower, its amplitudes are larger, and its phases are later than those of outer tidal flats. These suggest that Inchion coastal area may be divided into two areas: the tidal flats from Incheon harbor to Sorae, which is largely influenced by the seasonal variation of solar heating, precipitation and evaporation and the outer tidal flats, which is slightly influenced by the effects of seasonal variation of salinity.