Environmental pollutions caused by the release of wide range of compounds from various industries such as paper pulp and textiles have a serious effect on ecosystem and human health. Sulphonated azo dyes represent a large class of dyes used in textile industries. The precursors of these dyes are sulphonated aromatic amines. Release of such toxic compounds in the environment cause toxic effects on soil fertility and aquatic ecosystem. Limited attention has been paid towards the fate of sulphonated aromatic amines and substituted sulphonated aromatic amines in the environment previously. The present research work describes biodegradation of azo dye precursor 1- amino 2- napthol 4 - sulphonic acid by Pseudomonas desmolyticum NCIM 2112 which was studied by FTIR and GCMS analysis. The resulting metabolites of biodegradation include propylmethane thiosulfonate and aminobenzene and they were found to be nontoxic in the environment.