The Cannizaro reaction is a chemical reaction undergone by some aldehydes under basic conditions. It is an example of disproportionation in which the aldehyde is simultaneously reduced to an alcohol and oxidized to a carboxylate ion:

2 RCHO + OH^- → RCH₂OH + RCOO^-

Only aldehydes that cannot form an enolate ion undergo the Cannizaro reaction. Under the basic conditions that facilitate the reaction, aldehydes that can form an enolate instead undergo aldol condensation. Examples of aldehydes that can undergo a Cannizaro reaction include formaldehyde and aromatic aldehydes such as benzaldehyde.

The Cannizaro reaction is named for the Italian chemist Stanislao Cannizaro , who discovered it (using benzaldehyde) in 1853.