A new route for the indirect conversion of methane that makes use of the latest advance in methyl chloride production is reported. Acetic acid was produced from the carbonylation of methyl chloride by carbon monoxide over a variety of catalysts. The presence of promoters was crucial for the carbonylation reaction. The yield of acetic acid reached 84.7% with RhCl3 as catalyst and PPh3/KI as promoters. The effects of reaction temperature, carbon monoxide pressure, and reaction time were investigated. The possible reaction mechanism was discussed.