Clemmensen reduction is an organic reaction which leads to the formation of alkanes by reduction of aldehydes or ketones in presence of acid and with amalgamated zinc. The Danish chemist discovered this reaction named Erik Christian Clemmensen. The substrate should not be acid sensitive, if the substrate is acid sensitive then reduction is carried out by Wolff-Kishner reduction.

The mechanism of action is not exactly clear. There are two proposed mechanisms i.e. carbanionic mechanism where the attack of Zn is involved and carbenoid mechanism where Zn act as a surface to perform reaction and it is a radical process.