Alkylation of toluene was carried out on microporous salts of phosphotungstic acid. Among the systems studied, M2.5H0.5PW12O40 showed maximum catalytic activity. p-Xylene selectivity was evaluated as a function of x. A linear correlation was observed between para-selectivity and number of strong acid sites with strength of H0≤ -5.6. © Akadémiai Kiadó. All rights reserved.