A 1-D model for estimating eddy diffusivity coefficient of heat (K sub(h)) in the upper layers of the sea is proposed and tested using data collected along 68 degrees E and 52 degrees in the equatorial Arabian Sea. Diurnal range of sea surface temperature in this region is up to 0.4 degrees C with minimum temperature occurring at 0630 hrs IST and maximum temperature occurring at 1600 hrs IST. The value of K sub(h) is found to vary between 0.003 and 0.011 m sup(2)s sup(-1) with lower value in the Central Equatorial Arabian Sea (CEAS). A comparison of the model computed K sub(h) values with those estimated from the heat balance of the upper layer (50 m) of the sea shows good agreement in the region of weak winds (CEAS) or low turbulent mixing regime. Computed K sub(h) is found to be slightly lower than the estimated K sub(h) in the region of strong winds (Western Equatorial Arabian Sea) or high turbulent mixing regime