Abstract: A thermal decomposition process and apparatus of the fluidized bed type for organic solid materials, particularly organic solid waste material contained in urban rubbish comprising a fluidized bed thermal decomposition furnace, the interior of which is divided by a partition plate into two zones, namely a first zone for thermally decomposing the organic solid waste material in the absence of oxygen and a second zone mainly for burning the carbonized material produced as a result of thermal decomposition of the organic solid waste material. Non-condensable components of the gas resulting from the thermal decomposition of the organic solid waste material are recirculated as fluidizing gas into the first zone, while air is used as the fluidizing gas for the second zone. Heat for the thermal decomposition in the first zone is obtained from the combustion in the second zone and transferred by the intertransfer of fluidized solids between zones beneath the partition plate.