The effect of fluorine on the hydrogenation of cyclohexene over sulfided NiMo catalysts supported on Al2O3 and amorphous silica-alumina (ASA) was studied at 5.0 MPa and between 3 10 and 350degreesC. Fluorination was performed in situ after sulfidation of the catalyst. The hydrogenation of cyclohexene produced mainly cyclohexane over the Al2O3-supported catalysts. On the ASA-supported catalysts, large amounts of the isomerization products methylcyclopentene and methylcyclopentane were formed in addition to the hydrogenation product cyclohexane. At the applied partial pressure of cyclohexene between 16 and 100 kPa, the hydrogenation is between zero and first order in the partial pressure of cyclohexene on all catalysts. The Al2O3-supported catalysts showed higher conversions of cyclohexene than their ASA-supported counterparts. Fluorination mainly enhances the isomerization of cyclohexene to methyleyclopentene. Kinetic parameters were obtained by fitting the kinetic data with Langmuir-Hinshelwood rate equations in a wide range of conversions. The unchanged activation energy and heat of adsorption for the hydrogenation of cyclohexene to cyclohexane indicate that the active sites for hydrogenation are not influenced by, in situ fluorination. The activation energy for the isomerization of cyclohexene remained constant after fluorination. In situ fluorination introduces more acid sites for the isomerization reaction over both the Al2O3- and ASA-supported catalysts.