A series of samples of zeolite MFI with the same morphology, but different concentrations of Bronsted acid sites, have been obtained by means of ion exchange. Methods of temperature-programmed desorption of ammonia (TPD NH3) and IR spectroscopy of absorbed 2,6-di-tert-butylpyridine have demonstrated that the samples differ in the ratio of acid sites in the bulk of zeolite and on the external surface. Stability of the samples against deactivation has been determined in the oligomerization reaction of butylenes using the accelerated deactivation test under severe conditions. It has been shown that the main contribution to deactivation is made by acid sites located on the external surface of zeolite crystals.