An analytical study of the sea surface temperature at Thumba Equatorial Rocket Launching Station (Lat8°32'N, Long.76°52'E) at two different hours—0930 and 1130 hrs 1ST—for a period of three years (1967-1970) is presented. A few interesting features of the daily and monthly variation of sea surface temperature are discussed in reation to the onset and withdrawal of the Indian South-west monsoon. The sea surface temperature off Kerala coast is found to be below 26*C during the' south-west monsoon period (June to September) and its seasonal variation is in the range 22-30°C. The diurnal variation of the coastal sea water is found to be less significant (1-2°C) when compared to that of the canal water temperature (3-4°C) and surface air temperature (6-8°C). The standard deviation of sea, canal and surface air temperature is of the same magnitude 1 .S°C.