A novel type of crosslinkable poly(aryl ether sulfone)(PAES) bearing an allyl pendant(PES-OAllyl) was synthesized by a grafting reaction of hydrophenyl-containing PAES(PES-OH) and allyl bromide. PES-OH was pre- pared by a demethylation reaction of a methoxyphenylated PAES(PES-OCH) in the presence of pyridine/hydrochlo- ride. The PES-OCH was synthesized by an aromatic nucleophilic substitution of bis(4-chlorophenyl)sulfone and (p-methoxy)phenylhydroquinone. Both DSC and solubility investigation were used to study the crosslinking behavior of PES-OAllyl. After heat treatment, the glass transition temperature(T) value of PES-OAllyl sharply increased from 165 ℃ to 227 ℃. Meanwhile, PES-OAllyl changed from a soluble polymer to an insoluble thermoset. In addition, TGA(thermogravimetric analysis) result suggests that the thermal stability of the crosslinked product was improved. All the data prove that the crosslinked PES-OAllyl could be a potential solvent-resistance high-performance material.