A catalyst for acid-catalyzed hydrocarbon conversions, in particular for the alkylation of olefins with isoparaffins, containing a crystalline zeolite with an SiO.sub.2--Al.sub.2O.sub.3 molar ratio of <10, the alkali cations of which are at least partially replaced by H.sup.+ ions and/or polyvalent cations, the residual concentration of alkali cations amounting to less than around 0.2% by weight, the concentration of the Bronsted centers, determined as a function of the pyridine chemisorbed on the catalyst surface, amounting to around 0.1 to 4 mmol/g of catalyst, and the ratio between the concentration of the acid centers of the Bronsted type (B) and of the Lewis type (L), expressed as the surface ratio of the absorption bands at 1540 .+-.5 cm.sup.-1 (B) and 1450 5 cm.sup.-1 (L) after heating to a temperature of 450.degree. C amounting to around 1.4 or higher, is described.