Dehydration kinetics of sodium-light lanthanoid double sulfate monohydrates has been evaluated by applying two methods of different categories for the analysis of dynamic TG data. The Coats-Redfern integral and Achar differential methods gave similar results. The possible mechanism was found to be diffusion controlled. The apparent dehydration activation energies are in the range of approximate to 100-180 kJ mol(-1) and show an upward trend from La to Sm with the decreasing ionic radius of the Ln(3+) ion. The double salt structure with the smallest Ln(3+) ion is the most kinetically stable but the most thermodynamically unstable one towards the dehydration process.