Copolymers of styrene and chloromethylstyrene containing 2% ammonium salt groups have been grafted onto montmorillonite interlayers by cation exchange process. The remaining chloromethyl groups were modified to produce phosphonium salts. The catalytic activities of the phosphonium moieties supported on polystyrene-montmorillonite have been investigated in thiocyanate and nitrite nucleophilic reactions. The effectiveness of these catalysts has been examined under the effects of several factors governing the reactions rates such as the chemical composition of polymers backbone, chemical nature of the active moiety, degree of loading, nature of the solvent, and reaction temperature.