In this study, we revisit the photodissociation reactions of methyl formate in the T-1 and S-1 states. The geometries of the transition states of the dissociation channels to CH3O + HCO, CH3OCO + H, and CH3 + HCO2 in the S-1 and T-1 states are optimized at the CAS(10,8) level of theory with 6-311G(2df,2pd) and 6-31G(d,p) basis sets. According to the CASPT2 calculations, the dissociation to CH3O + HCO on the S-1 surface is the dominant reaction in the photodissociation of methyl formate, and the dissociation to CH3 + HCO2 on the S-1 surface is the minor one. (c) 2011 Elsevier B.V. All rights reserved.