L-ornithine is an optically active form of ornithine having L-configuration. It has a role as a hepatoprotective agent, an algal metabolite and a mouse metabolite. It is an ornithine and a non-proteinogenic L-alpha-amino acid. It is a conjugate base of a L-ornithinium(1+). It is a conjugate acid of a L-ornithinate. It is an enantiomer of a D-ornithine.