α-Aminobutyric acid (AABA), also known as homoalanine in biochemistry, is a non-proteinogenic alpha amino acid with chemical formula C4H9NO2.

Homoalanine is biosynthesized by transaminating oxobutyrate, a metabolite in isoleucine biosynthesis.

One example of a nonribosomal peptide containing homoalanine is ophthalmic acid, which was first isolated from calf lens.

The two other are the neurotransmitter γ-aminobutyric acid (GABA) and β-aminobutyric acid (BABA) which is known for inducing plant disease resistance.

This amino acid has been detected in meteorites.