Ester hydrolysis is promoted both by acid and basic conditions. Acid conditions catalytically enhance the reaction with the addition of a proton to the carbonyl oxygen of the ester group. This enhances the reactivity of the carbonyl group to nucleophilic attack by increasing its electron with-drawing character. Acid catalysis helps a subsequent step as well, with the addition of a second proton to increase the facility of the alkoxy portion to leave as an alcohol.

Alternately, basic conditions may also promote ester hydrolysis. Base promoted ester hydrolysis is also called saponification, occurring with the hydroxide anion acting as the nucleophile. Saponification can be used to produce fatty acid salts (soap) from triglyceride.