In enzymology, a succinate-semialdehyde dehydrogenase (SSADH) (EC 1.2.1.24) is an enzyme that catalyzes the chemical reaction The 3 substrates of this enzyme are succinate semialdehyde, NAD+, and H2O, whereas its 3 products are succinate, 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 succinate-semialdehyde:NAD+ oxidoreductase.

Succinate-semialdehyde dehydrogenase is found in organisms ranging across the tree of life from bacteria to humans.

In bacteria, the enzyme is also involved in γ-aminobutyric acid degradation, but can be recruited to facilitate other functions, such as converting succinate-semialdehyde formed during fission of the pyridine ring to succinic acid for entry into the Krebs Cycle.