The kinetics of the dehydration of Ha-dong kaolin was studied isothermally at various temperatures. Dehydration rate was measured by thermogravimetry method in the temperature range of 440~50$0^{circ}C$ and the particle size range of 170~325mesh. The general equation f($alpha$)=kt, where $alpha$ is the fraction reacted in the time and the function f($alpha$) depends on the reaction mechanism, was applied to this reaction. The function, f($alpha$) was obtained by application of reduced-time plot and plot of lnln (1-$alpha$) vs. ln (time), and expressed as (1-$alpha$) ln (1-$alpha$)+$alpha$=kt. The dehydration followed the diffusion-controlled reaction model and gave activation energy of 30Kcal/mole.