PURPOSE: To produce the titled compound keeping the catalytic activity, by carbonylating an O-methyl compound in a reaction liquid containing a carboxylic acid in the presence of a hydrogenated Rh catalyst and an Al compound accelerator.

CONSTITUTION: An O-acetyl compound (e.g. acetic anhydride) is produced by carbonylating an O-methyl compound (e.g. methyl acetate) with carbon monoxide mixed with 1W30% hydrogen, in a reaction liquid containing ≥1mol/l carboxylic acid, in the presence of an Rh catalyst and an iodine compound (preferably methyl iodide), using an Al compound as a reaction accelerator. The atomic ratio of Al to Rh is about 5W50. The concentration of the Al compound in the reaction liquid is ≥0.1mol/l, especially 0.2W0.5mol/l for attaining sufficient effect.