Acetaldehyde dehydrogenase (eg. EC 1.2.1.10) is a dehydrogenase enzyme that converts acetaldehyde into acetic acid. The EC number of acetaldehyde dehydrogenase is 1.2.1.10.

The oxidation of acetaldehyde to acetate can be summarized as follows:

CH₃CHO + NAD⁺ CoA → + acetyl-CoA + NADH + H⁺

In the liver, the enzyme alcohol dehydrogenase oxidizes ethanol into acetaldehyde, which is then further converted into the harmless acetic acid by acetaldehyde dehydrogenase. Acetaldehyde is more toxic than alcohol and is responsible for many hangover symptoms. N-acetylcysteine (NAC) is known to assist in processing acetaldehyde in the body and therefore can help to relief hangover symptoms.

Some persons from far-Eastern descent have a mutation in their acetaldehyde dehydrogenase gene, making this enzyme less effective. In these people, acetaldehyde accumulates after drinking, leading to severe and immediate hangover symptoms. These people are therefore less likely to become alcoholics. The drug antabuse (disulfiram) also prevents the oxidation of acetaldehyde to acetic acid, with the same unpleasant effects for drinkers. It is used in the treatment of certain alcoholics.