Gas phase cracking of methyl tert-butyl ether (MTBE) was carried out over two types of macroreticular resin catalysts, Amberlyst 15 and Amberlyst XN1010. Experiments were controlled so that the resistance to the external mass transfer could be neglected. The rate of cracking was first order to the MTBE concentration for both catalysts. The selectivity to isobutylene and methanol as well as the cracking activity were higher for Amberlyst XN1010 than for Amberlyst 15. The catalylic activities of other acid catalysts, i.e, silica-alumina, γ-alumina(silicated), HY-zeolite and H-mordenite, were compared with those of the two macroreticular resin catalysts, and their relative differences were discussed in terms of the acid strength, the acidity, and the sieving effect.