甲磺酸酯(mesylate、甲磺酸、甲磺酸盐)在化学上是指所有的"甲磺酸"(CH₃SO₃H)盐或酯。在盐里，甲磺酸酯是以"CH₃SO₃"的阴离子形式存在的。当辩证医药品所含有的基(官能团和自由基)或"阴离子"(anion)之国际非专利药品名称时，甲磺酸酯(mesylate)正确的拼写是甲磺酸(mesilate，"甲磺酸伊马替尼"(imatinib mesilate)、又为"伊马替尼甲磺酸")。

甲磺酸酯是有机化合物的基(团)且共享着一般的结构CH₃SO₂O−R(简称MsO−R)的普通官能团，其中R是一种"有机取代物"(organic substituent)。甲磺酸酯在亲核取代反应上被认为是一种极佳的离去基团。

In chemistry, a mesylate is any salt or ester of methanesulfonic acid (CH₃SO₃H). In salts, the mesylate is present as the CH₃SO₃ anion. When modifying the International Nonproprietary Name of a pharmaceutical substance containing the group or anion, the correct spelling is mesilate (as in imatinib mesilate, the mesylate salt of imatinib).