Lignin is the major source of polyphenolic compounds available from natural biomass. Although most commercial lignin products have been supplied from wood biomass, the residues from bioethanol production processes could be an additional potential source. About 75% of lignin inherent in corn stover and rice straw was recoverable from the residues of bioethanol producing processes. Chemical structures and thermolysis features of the lignin residues from corn stover and rice straw obtained through acid-alkali pretreatments were characterized. Due to inherent structural differences, the corn stover- and rice straw lignin were more reactive and had less thermal stability than the wood-based Kraft lignin. The corn stover lignin showed the lowest maximum degradation temperature with the highest mass loss rate in the primary pyrolysis reaction and it was mainly pyrolyzed into monomers of lignin building blocks with a higher phenol content (10%), unlike the other lignin samples (<6%). (C) 2014 Elsevier B.V. All rights reserved.