Abstract: The o-methylation of phenol with DMC to anisole over KBr catalyst was studied by in-situ FT-IR, thermodynamic analysis and reactivity test. FT-IR showed that phenol was activated to generate phenolate over 100℃ while DMC was not activated even at 200℃ by KBr catalyst. Anisole was formed over 150℃ on KBr catalyst as FT-IR and reactivity data revealed. Small amount of carboxymethylation product methyl phenyl carbonate (MPC) was detected and its formation was earlier than that of anisole. Thermodynamic analysis and MPC decomposition experiment showed that the reaction of MPC formation was a parallel and reversible side reaction. Methylation reaction mechanism was thus suggested as phenol was activated by KBr to form phenolate, a strong nucleophilic reagent, which attacked DMC methyl carbon to generate anisole when temperature was higher than 150℃.