In enzymology, a valine decarboxylase (EC 4.1.1.14) is an enzyme that catalyzes the chemical reaction

L-valine ${\displaystyle \rightleftharpoons }$ 2-methylpropanamine + CO₂

Hence, this enzyme has one substrate, L-valine, and two products, 2-methylpropanamine and CO₂.

This enzyme belongs to the family of lyases, specifically the carboxy-lyases, which cleave carbon-carbon bonds. The systematic name of this enzyme class is L-valine carboxy-lyase (2-methylpropanamine-forming). Other names in common use include leucine decarboxylase and L-valine carboxy-lyase. It employs one cofactor, pyridoxal phosphate.

• Sutton CR, King HK (February 1962). "Inhibition of leucine decarboxylase by thiol-binding reagents". Archives of Biochemistry and Biophysics. 96 (2): 360–70. doi:10.1016/0003-9861(62)90421-6. PMID 13918558.