Abstract: The invention relates to a process for the simultaneous treatment of solid or semi-solid organic waste and liquid organic waste with a view to the simultaneous production of compost and biogas.According to this process, said liquid organic waste is subjected to a liquid-solid separation, the liquid phase from this separation is subjected to anaerobic fermentation in at least one closed digester, the solid phase from said liquid-solid separation is mixed with said solid or semi-solid organic waste, the resulting mixture is subjected to aerobic fermentation at the periphery of said digester and in contact therewith and mud, clarified liquid and gas are respectively discharged from said digester whereas compost from the aerobic fermentation of said solid or semisolid waste is recovered at the periphery of said digester.