脱氨作用（英语：Deamination，亦可称为脱氨基或去胺作用）是指移除分子上的一个氨基。人类的肝脏经由脱氨作用将氨基酸分解，当氨基酸的氨基被去除之后，会转变成氨。由碳及氢所组成的残余部分，则回收或氧化产生能量。对人体而言，氨具有毒性，因此某些酵素将会在尿素循环中将二氧化碳分子附加其上，使氨转变成尿素或尿酸。之后这些尿素及尿酸再经由尿液排出体外。

除了氨基酸之外，DNA的构成物之一胞嘧啶也会因为脱氨作用而转变成尿嘧啶；胞嘧啶受到甲基化之后的产物5-甲基胞嘧啶，则会在脱氨作用下转变成胸腺嘧啶。

Deamination is the removal of an amine group from a molecule. Enzymes that catalyse this reaction are called deaminases.

In the human body, deamination takes place primarily in the liver, however glutamate is also deaminated in the kidneys. Deamination is the process by which amino acids are broken down if there is an excess of protein intake. The amino group is removed from the amino acid and converted to ammonia. The rest of the amino acid is made up of mostly carbon and hydrogen, and is recycled or oxidized for energy. Ammonia is toxic to the human system, and enzymes convert it to urea or uric acid by addition of carbon dioxide molecules (which is not considered a deamination process) in the urea cycle, which also takes place in the liver. Urea and uric acid can safely diffuse into the blood and then be excreted in urine.