The effects of halogenation of polystyrene sulfonic acid resins on acidic and catalytic properties have been evaluated. Four polystyrene-co-divinylbenzene sulfonic acid resins from Rohm and Haas (Amberlyst 70, Amberlyst 15, Amberlyst 35 and Amberlyst 36) have been characterised in terms of their acidities (both strength and acid site concentrations) by ammonia adsorption flow microcalorimetiy, their thermal and hydrothermal stabilities, and their catalytic activities in two test reactions, the isomerisation of alpha-pinene and the benzylation of toluene using benzyl alcohol. Amberlysts 35 and 36 are "over-sulfonated" and exhibit stronger acid sites than the conventional sulfonated resin Amberlyst 15. These acid properties explain differences in catalytic activities, although differences between the porosities of Amberlysts 35 and 36 have a profound affect on catalytic performance in non-polar reaction media. Amberlyst 70, which is reported to be halogenated and is claimed to exhibit better thermal stability than the other three resins, shows acid site strengths similar to those of the over-sulfonated Amberlysts 35 and 36, and shows significantly better thermal and hydrothermal stability. It exhibits a relatively low pore volume, however, constraining its catalytic activity in non-swelling solvents. (c) 2007 Elsevier B.V. All rights reserved.