An NAD-linked 2-carboxybenzaldehyde dehydrogenase which catalyzes the conversion of 2-carboxybenzaldehyde to o-phthalate was isolated and purified about 130-fold from the cell extract of Alcaligenes faecalis AFK2 which was grown on phenanthrene. The purified enzyme had a molecular weight of about 160, 000, and consisted of four molecules of a single kind of polypeptide having a molecular weight of 40, 000. It showed high specificity for 2-carboxybenzaldehyde as its substrate and for NAD as its electron acceptor. The K_m values for the substrate and NAD were 5.4×10^-5 and 1.4×10^-4M, respectively. Because of the increase in the enzyme level by the growth on phenanthrene, the enzyme was inducible, suggesting its responsibility for the degradation of phenanthrene in Alcaligenes faecalis AFK2.