Polystyrene of different molecular weights in emulsified solution was used for the preparation of polystyrene-hydroperoxide，the intrinsic viscosity and HPO-value (the average number of hydroperoxyl groups per 1000 monomeric units of polystyrene) of which were then determined．A wide absorption band in the region of 3200--3600 cm-1 attributed to the hydroperoxyl group was observed in the infrared absorption spectra of the polystyrene-hydroperoxide；its absorption intensity became more marked with increas-ing HPO-value．The polymeric hydropetoxide was then used for the initiation of vinyl monomers，e．g．styrene and methyl methacrylate respectively，and the final products after purification were identified as graft copolymers by the following ways： (1)turbidimetric titration， (2)determination of thermomechanical curve， (3)determination of exchange capacity of the copolymers after alkaline hydrolysis，and (4) infrared absorption spectra．