Malonyl chloride is the organic compound with the formula CH<sub>2</sub>(COCl)<sub>2</sub>. It is the acyl chloride derivative of malonic acid. It is a colorless liquid although samples are often deeply colored owing to impurities. The compound degrades at room temperature after a few days. It used as a reagent in organic synthesis.
Malonyl chloride can be synthesized from malonic acid in thionyl chloride. As a bifunctional compound, it is used in the preparation of a number of cyclic compounds by diacylation. Heating in the presence of non-nucleophilic base gives the ketene derivative O=C=C(H)COCl.