Deactivation of several Ni catalysts supported on a K-clinoptilolite containing iron species was analyzed in the hydrogenation of ethylbenzene in the presence of thiophene. The location and coordination of iron in the zeolite was modified by different thermal treatments given to the catalysts. Studies by ESR showed that the state of iron affects the nature and strength of the iron-nickel interaction. Experimental results indicated the existence of a correlation between that interaction and the resistance of the catalysts to thiophene poisoning, in such a way that the stronger the iron-nickel interaction the higher the sulfur resistance. An interpretation of the differences in sulfur resistance of the catalysts based on the formation of surface electron-deficient Ni species by interaction of Ni particles with Fe3+ of the zeolite is discussed.