Data are reported for the chemical analysis of the solid residues of supercritical extraction of Populus tremoloïdes in methanol. The lignin content is determined by the thioglycolic acid test as the Klason test is shown to yield an estimation of recondensed material in addition to lignin. The TFA acid hydrolyzates of SCE solid residues were analysed for simple sugars by HPLC. The results indicate that hydrolyzable material contains products of thermal degradation of polysaccharides.