Kinetics and catalyst deactivation have been studied for methyl formate synthesis by methanol carbonylation. In a liquid phase reaction, alkali catalysts drove the methanol carbonylation rapidly to equilibrium and showed almost 100% selectivity to methyl formate. A kinetic study showed that the reaction was of first order both in methanol and CO concentrations. The rate depended on alkali metal of the catalyst in the order, K>Na>Li. A rate equation was derived from a mechanism which assumed that alcoholate ion was the active catalytic intermediate. The equation fitted the experimental data satisfactorily. The catalyst was indeed sensitive to the small amount of H₂O or CO₂ added to the reaction mixture. It was almost completely deactivated when more than a stoichiometric amount of H₂O or CO₂ relative to the amount of the catalyst was added.