The introduction of chloromethyl group was evaluated for ethyleneglycol dimethacry- late (EGD) or butanediol dimethacrylate(BDD) 2n crosslinked polystyene as crosslinked polyst- yrene was chloromethylated with methylal as solvent- The effect of local concentration might be expected to affect the induction of chloromethyl group and autocrosslinking, so it was concluded that the induction of chloromethyl group was inhibited in EGD and BDD crosslinked polystyrenes even though they have very Barge swelling ratio by solvent. When the mixed solvent of dichloroethane/methylal was used, the autocrosslinking was hardly occurred even in 40'I reaction. And it was proved that the decreased concentration of methylal which was absorbed inner part of crosslinked polystyrene bead by mixed solvent restrained the sudden introduction of chloromenthyl group, but also the autocrosslinking between chloromethyl group.