Process for decontaminating, cleaning a solid organic substrate contaminated by solid radioactive particulate inorganic contaminants, in which: the said solid substrate is brought into contact with an extraction medium, devoid of water, comprising: dense pressurized CO.sub.2; at least one nonhalogenated surface-active compound chosen from block copolymers of poly(ethylene oxide) PEO and poly(propylene oxide) PPO, such as (EO).sub.x-(PO).sub.y diblock copolymers, (EO).sub.x-(PO).sub.y-(EO).sub.x triblock copolymers and (PO).sub.x-(EO).sub.y-(PO), triblock copolymers, where x and y are integers from 2 to 80 with x other than y; and polydi(1 to 6C)alkylsiloxanes, such as polydimethylsiloxane (PDMS); and at least one complexing agent chosen from tributyl phosphate (TBP), crown ethers, tributylphosphine oxide, triphenylphosphine oxide and tri(n-octyl)phosphine oxide; the solid substrate and/or the extraction medium is/are subjected, simultaneously with the contacting operation, to a mechanical action.