In enzymology, an aliphatic nitrilase also known as aliphatic nitrile aminohydrolase () is an enzyme that catalyzes the hydrolysis of nitriles to carboxylic acids:
Thus, the two substrates of this enzyme are an aliphatic nitrile (R-CN) and H<sub>2</sub>O, whereas its two products are a carboxylic acid (R-COOH) and NH<sub>3</sub>.
This enzyme belongs to the family of hydrolases, those acting on carbon-nitrogen bonds other than peptide bonds, specifically in nitriles. This enzyme participates in styrene degradation.