Abstract: The pyrolysis mechanism of levoglucosan (one of the major product from cellulose pyrolysis) was investigated by using density functional theory at B3LYP/6-31++G(d,p) level. Four possible reaction pathways were proposed and the geometries of reactant, transition states, intermediates and products for each pathway were fully optimized; the standard thermodynamic and kinetic parameters of each reaction at different temperatures were calculated. The results showed that levoglucosan is converted to intermediate IM₁ via transition state TS₁ with an activation energy of 296.53 kJ/mol by breakage of C(1)-O(7) and C(6)-O(8) hemiacetal linkages and formation of C(5)-C(6)-O(7) circular structure, and then IM₁ is converted to intermediate IM₂ via transition state TS₂ with an activation energy of 234.09 kJ/mol. IM₂ can be further decomposed via four different pathways. Pathways 1 and 4 involve decarbonylation reactions with high energy barriers, and as a result, they are unlikely to occur; on the other side, the energy barriers for the rate-determining steps of pathways 2 and 3 are much lower, which are kinetically favorable and possible the major reaction channels for IM₂ pyrolysis.