A process for the isomerization of a para-xylene depleted, meta-xylene rich stream under at least partially liquid phase conditions using ZSM-23 with an external surface area of at least 75 m2/g (indicating a small crystallite size), and a SiO2/Al2O3 ratio between 15 and 75 that produces a higher than equilibrium amount of para-xylene, i.e., more than about 24 wt % of para-xylene, based on the total amount of xylenes.