Alkaline hydrolysis reaction of heterocyclic auto disperse dyes was discussed and reaction mechanism was proposed. The FT-IR spectra of auto dye derived from dichlorobenzothiazole and its hydrolysis product were almost the same suggesting the dye was stable for alkali. However, auto dyes derived from nitrothiazole and dinitrothiophene were very rapidly hydrolyzed by alkali with large hypsochromic and hypochromic shifts. Their hydrolyzed products were water-soluble and different from those of the original dyes. Molecular weights of the hydrolyzed products were about half of those of the original dyes. Their hydrolysis mechanism may be explained by the rapid nucleophilic attack of OH- on the carbon adjacent to auto group, electron density of which decreased due to the strong electron-withdrawing group such as vitro group.