Abstract: The present invention describes halogenated polymer resins stabilized with a stabilizer comprising a synthetic crystalline aluminosilicate of the formula M.sub.2/n O.Al.sub.2 O.sub.3.ySiO.sub.2.wH.sub.2 O, in which M is a charge balancing cation, n is the valence of M and is 1 or 2, y is the number of moles of SiO.sub.2 per mole of Al.sub.2 O.sub.3, and is 1.85 to 15 with a preferred range of about 2 to 5, and w is the moles of water of hydration per molecule of said aluminosilicate, wherein said aluminosilicate has a mean crystallite size in the range of about 0.01 .mu.m to about 1 .mu.m and a mean particle size in the range of about 0.1 to 10 .mu.m. Also described is a method for stabilizing halogenated polymers such as PVC and CPVC by incorporating said aluminosilicate into a formulation thereof.