In chemistry, a mesylate is any salt or ester of methanesulfonic acid (CH₃SO₃H). In salts, the mesylate is present as the CH₃SO₃⁻ anion.

Mesylate esters are a group of organic compounds that share a common functional group with the general structure CH₃SO₂O-R where R is an organic substituent. Mesylate groups are considered excellent leaving groups in nucleophilic substitution reactions.

Mesyl is the term for the methanesulfonyl or CH₃SO₃- functional group.

functional groups