Four possible channels of glycerol unimolecular pyrolysis were investigated theoretically by means of the quantum chemistry calculation based on density functional theory. Energy barriers and reaction rate constants were employed to analyze the possible pyrolysis mechanisms. Mechanism A was the most possible channel for glycerol pyrolysis based on the calculated results. According to this mechanism, C-2 of glycerol transferred into acetaldehyde as its aldehyde group carbon atom following the Cyclic Grob Fragmentation. The rate constants for mechanism B-p2-1 which transferred C-2 of glycerol into acetaldehyde as its methyl group was three orders magnitude lower than that of mechanism A. The above information should be useful to understand the pyrolysis mechanism of more complex carbohydrates such as glucose and cellulose. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.