Cationic polymer latexes were prepared by emulsion copolymerization of vinylbenzyl chloride and divinylbenzene followed by quaternization with trimethylamine and used as catalyst supports for 5,10,15,20-tetrakis(2, 6-dichloro-3-sulfonatophenyl)porphinatomanganese(III) chloride and 5,10,15,20-tetra(4-sulfonatophenyl)porphinatomanganese(III) chloride. The supported catalysts and water soluble analogues were used for oxidation of styrene, 1-decene and cis-cyclooctene by hydrogen peroxide and tert-butyl hydroperoxide in the aqueous phase. The oxidation of 1-decene and cis-cyclooctene failed. In the oxidation of styrene, the porphyrin catalysts in the latex were more active than in solution. The relative molar ratios of oxidant: styrene: Mn porphyrin were 1250: 750: 1, and about 25% styrene conversion in 4 h was obtained. When hydrogen peroxide was employed as oxidant, styrene oxide and benzaldehyde were the major and minor products, respectively, and in the case of tert-butyl hydroperoxide, it was vice versa. The reaction depended on pH, the porphyrin ligand, type of oxidant used and presence of imidazole.