3-Methylcrotonyl-CoA (ò-Methylcrotonyl-CoA or MC-CoA) is an intermediate in the metabolism of leucine.
It is found in mitochondria, where it is formed from isovaleryl-coenzyme A by isovaleryl coenzyme A dehydrogenase. It then reacts with CO<sub>2</sub> to yield 3-methylglutaconyl-CoA, catalysed by 3-Methylcrotonyl-CoA carboxylase.