A 3-nitrobenzenesulfonic acid (3-NBS)-degrading bacterium was isolated from a batch enrichment culture containing 3-NBS and yeast extract, and identified as an Alcaligenes sp. In a batch degradation test, the isolate, named GA-1, utilized 3-NBS as a growth substrate with stoichiometric accumulation of sulfate ions, and consumed most of the dissolved organic carbon (DOC) which originated from 3-NBS in the culture. A trace amount of sulfite ions was also detected on an agar test plate of mineral salts (MS) medium containing 3-NBS and Ellman’s reagent (5,5’-dithiobis[2-nitrobenzoic acid]), which reacts sensitively with free sulfite ions to develop a yellow coloration. These results indicate that 3-NBS was effectively desulfonated and mineralized by strain GA-1 with the release first of sulfite ions, which were then oxidized immediately to sulfate ions.