Manganese(II) dicarboxylate hydrates Mn[OOC(CH2)(n)COO]. xH(2)O have been prepared by the addition of MnCO3 powder or concentrated MnSO4 solution to aqueous solutions of the corresponding dicarboxylic acids. The crystal forms of the precipitated compounds were observed by optical microscopy. The crystals were obtained either as ellipsoidal, short rods or very small uneven particles. The crystals were different from those of the dicarboxylic acids. The dicarboxylates obtained were characterized by X-ray diffraction analysis and IR spectral measurement. The thermal dehydrations of the Mn(II) dicarboxylate hydrates were investigated by TG-DTA. The temperatures at which dehydration occurred were taken as a measure of the strength of the Mn-OH2 bond, and these were found to vary with increasing number of CH2 groups in the dicarboxylic acid. The kinetic parameters for the dehydration were calculated by employing a computation method. The three-dimensional diffusion model is found to be the best for describing the kinetic results for the main reaction.