The invention relates to a process for producing a desired dialkylbenzene isomer having a formula R.sub.2C.sub.6H.sub.4, where R is an alkyl substituent, by contacting a polyalkylbenzene compound of formula R.sub.nC.sub.6H.sub.6-n, where n is an integer between 2 and 4, with a monoalkylbenzene compound of formula RC.sub.6H.sub.5 in the presence of a molecular sieve catalyst under reaction conditions sufficient to produce said dialkybenzene isomer. The preferred molecular sieve catalysts have pores or surface cavities greater than 5.6 Angstroms in diameter and/or an X-ray diffraction pattern including d-spacing maxima at 12.4.+-.0.25, 6.9.+-.0.15, 3.57.+-.0.07, and 3.42.+-.0.07 Angstrom.