Hydroisomerization and hydrocracking of n-heptane on sulfided NiW catalysts, supported on alumina modified with various amounts of fluoride, have been studied at 673, 698, and 723 K and at a total pressure of 3 MPa. It was found that alumina fluoridation increases the catalytic activity for both hydroisomerization and hydrocracking and provides a higher hydroisomerization selectivity, Differences in product selectivities for the hydroisomerization and hydrocracking of n-heptane indicate that alumina fluoridation induces also changes in the various contributions of the mechanisms involved in the transformation of n-heptane, A decrease in the ratio of 3-MC6 and 2-MC6 monobranched isomers predicted by a branching mechanism via the protonated cyclopropane (PCP) intermediates and a decrease in the dimerization cracking mechanism in favor of the classic bifunctional cracking mechanism were observed with increasing fluoride content, Theses changes are results of a better balance of the (de)hydrogenation and acidity functions of the sulfided catalysts with increasing fluoride content since the incorporation of fluoride increases the (de)hydrogenation function and decreases the strength of the acid sites.