According to a method for producing acetic acid by carbonylation of methanol characterized in that an acid having an acid dissociation constant (pKa) smaller than the constant of acetic acid is allowed to be present in the reaction system, acetic acid can be produced by the reaction of methanol and carbon monoxide in a reaction liquid in the presence of a solid catalyst containing rhodium and alkyl iodide, to achieve an enhanced reaction rate of carbonylation of methanol in producing acetic acid in the region at a high carbonylation degree (Ca>0.8 mol/mol) for more efficient production of acetic acid.