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Acetic formic anhydride, or ethanoic methanoic anhydride is a chemical compound with formula C₃H₄O₃, or H₃C-(C=O)-O-(C=O)H. It can be viewed as the mixed anhydride of acetic acid (H3C- (C=O)OH) and formic acid (H(C= O)OH) by removal of a molecule of water.
It can be produced by reaction between sodium formate and acetyl chloride in anhydrous diethyl ether, at 23–27 °C.Among other uses, it is a formylation agent for amines, amino acids, and alcohols, and a starting material for formyl fluoride.

O-Formyl Acetate is an formylation agent for amines, amino acids and alcohols.