Abstract: A process for treating oils and solvents contaminated by radioactive substances includes a step of subjecting the oils and solvents to the action of pre-selected micro-organisms in the presence of air and a very large volume of water, relative to the volume of oils and solvents to be treated. The micro-organisms destroy organic molecules, and in particular transform them into CO.sub.2 and H.sub.2 O. Further steps of the process include preparing a predetermined volume of water having predetermined characteristics of dissolved oxygen concentration, pH and redox potential and adding a predetermined charge of oils and solvents contaminated by radioactive substances to this volume of water, the charge corresponding to a volume of oils and solvents which is a predetermined fraction of the predetermined volume of water. The charge is subjected to the action of micro-organisms at a predetermined temperature and for a predetermined time period.