Five possible pyrolytic pathways of guaiacol were proposed with an emphasis on the reactivity of the methoxy group. Pathway 1 is about the homolysis of O-CH3. Pathways 2-4 focus on the demethoxylation of guaiacol. Pathways concerns the O-CH3 rearrangement. Standard thermodynamic and kinetic parameters of each reaction pathway were calculated at different temperatures based on density functional theory methods by using Gaussian 03 package at B3LYP/6-31G++(d,p) level. According to the calculation results, the five reaction pathways were ranked as Path 3, Path 1, Path 4, Path 2 and Path 5, in descending order of reactivity. Kinetic analyses results of the three demethoxylation reaction pathways (Path 2, Path 3 and Path 4) indicate that coupling a hydrogen radical to the carbon atom to which the methoxyl group bond can effectively lower the reaction energy barrier that existed in the process of demethoxylation. Pathway 5 demonstrates the possible formation mechanism of o-quinonemethide which is the key polymerization intermediate during lignin pyrolysis process. (C) 2014 Elsevier B.V. All rights reserved.