Chemical and textural characteristics of porous styrene-divinylbenzene copolymers beads as a function of chlorosulfonation reaction parameters have been investigated. Reaction time and temperature were varied throughout this study using 20, 40 and 60 wt% chlorosulfonic acid solutions in dichloroethane as chlorosulfonating agent. No change in the porous volume and particles size was observed but the specific surface area decreased similarly for all acid concentration. Chemical analysis showed that both chlorosulfonyl and sulfonyl products are obtained and the ratio between the two grafted groups varies as a function of reaction conditions. A maximum total group content of 4.8 meq/g was reached for 8 hours reaction at 60 degrees C with 40 wt% acid solution in the reaction. At higher acid concentration (60%), important undesirable sulfone bridging side reaction was found to occur during the chlorosulfonation process.