Abstract: The invention relates to a process for making acetyl chloride by reacting methoxy chloride with carbon monoxide under practically anhydrous conditions, at temperatures of 350.degree. to 575.degree. K, under pressures of 1 to 300 bars, and in the presence of a catalyst system containing at least one of the noble metals selected from rhodium, palladium, iridium or their compounds, iodine and/or its compounds and optionally trialkylphosphine oxide or triarylphosphine oxide, as well as an inert organic solvent. The invention provides more specifically for the reaction to be effected in the presence of a catalyst system containing n-heptane as the inert solvent and as additional ingredients methyltrialkyl phosphonium iodide and/or methyltriarylphosphonium iodide and at least one compound of chromium, molybdenum or tungsten.