In enzymology, a gamma-guanidinobutyraldehyde dehydrogenase (EC 1.2.1.54) is an enzyme that catalyzes the chemical reaction

4-guanidinobutanal + NAD⁺ + H₂O ${\displaystyle \rightleftharpoons }$ 4-guanidinobutanoate + NADH + 2 H⁺

The 3 substrates of this enzyme are 4-guanidinobutanal, NAD⁺, and H₂O, whereas its 3 products are 4-guanidinobutanoate, NADH, and H⁺.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the aldehyde or oxo group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is 4-guanidinobutanal:NAD+ 1-oxidoreductase. Other names in common use include alpha-guanidinobutyraldehyde dehydrogenase, 4-guanidinobutyraldehyde dehydrogenase, and GBAL dehydrogenase. This enzyme participates in urea cycle and metabolism of amino groups.