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 m² 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 °C. The catalysts obtained by deposition of the iridium phase on MgF₂, MgO and MgF₂–MgO (62 mol% MgO) calcined at 400–700 °C, have been tested in the reaction of hydrodesulfurization of thiophene. The most active has been the iridium catalyst supported on MgF₂–MgO.