The oxypropylation of rapeseed cake residue generated in the biodiesel production process was studied. The reaction was carried Out by suspending the rapeseed cake residue in propylene oxide [30/70 ratio (w/v)] in the presence of a basic catalyst (10% KOH) and heating the resulting mixture at 160 degrees C in a nitrogen atmosphere. The chemical structure of the obtained polyol was studied by CHNS elemental analysis, infrared spectroscopy, and H-1 NMR spectroscopy, and other parameters such as viscosity, OH number, molecular weight (GPC), and thermal behavior (DSC, TGA) were also measured. The obtained results showed an almost total conversion of the solid substrate into a polyol with good characteristics (OH number, 610 mg of KOH/g; viscosity, 84.23 Pa center dot s; and molecular weight, 33550 g/mol) for use in polyurethane, polyether, or polyester formulations.