Abstract: The kinetics of polymerization for concontratcd aqueous solutions of formaldehyde catalyzed by tin tctrachloride has been investigated. It is demonstrated that the reaction is a first order reaction both for the monomer and the calalyst. Its total activation energy is -2.1 Kcal/moic.It can be concluded that the polymerization of formaldehyde in the aqueous solutions is a reaction of ionic polymerization, which is catalyzed by Lewis acid produced in the presence of tin telrachloride; a reaction mechanism is suggested, and the rate equation Y_M = k[C][M] in good agreement with the experimental results is derived.