High molecular weight poly(phenylene sulfide) (PPS), M(w) > 2 x 10(5)) was synthesized via a poly(sulfonium cation) through oxidative polymerization of methyl 4-(phenylthio)phenyl sulfoxide. Polymerization proceeds in protic acid homogeneously. The poly(sulfonium cation) was soluble in common solvents such as formic acid and dimethyl sulfoxide. It was feasible to obtain high molecular weight poly(arylene sulfide) through the S(N)2 reaction with pyridine as nucleophile. The poly(sulfonium cation) was available as a soluble intermediate for the synthesis of high molecular weight poly(phenylene sulfide).