A catalytic process is provided for isomerizing an isomerization feed containing an aromatic C.sub.8 mixture of ethylbenzene and xylene in which the para-xylene content is less than equilibrium which comprises contacting said feed, under conversion conditions, with a catalyst comprising a crystalline aluminosilicate zeolite having a crystal size of at least about 1 micron, a silica to alumina ratio of at least about 12 and a constraint index, as hereinafter defined, within the approximate range of 1 to 12 to yield an isomerization product characterized by a reduced ethylbenzene content and an enhanced para-xylene content.