A mixed MgF2-MgO system has been tested as a potential support of iridium catalysts in the hydrodesulfurization of thiophene. Samples of MgF2-MgO with different contents of MgO (0-100%) have been prepared by one-step sol-gel method in the reaction of magnesium methoxide dissolved in methanol with hydrofluoric acid. They have been used as supports for the synthesis of iridium (1 wt% Ir) catalysts. The supports have been characterized by XRD, low temperature nitrogen adsorption and thermogravimetric measurements. The one-step method of MgF2-MgO synthesis has been shown to permit the control of MgO content in the mixed system. The MgF2-MgO samples are classified as mesoporous, of large surface area (100-450 m(2) g(-1)) depending on the amount of MgO introduced, with the maximum for 71 mol% MgO. The presence of two phases in the mixture delays the process of both MgF2 and MgO crystallization and increases the resistance of the MgF2-MgO texture to treatment at temperatures up to 800 A degrees C. The catalysts obtained by deposition of the iridium phase on MgF2, MgO and MgF2-MgO (62 mol% MgO) calcined at 400-700 A degrees C, have been tested in the reaction of hydrodesulfurization of thiophene. The most active has been the iridium catalyst supported on MgF2-MgO.