The indigoid-type dyes based on isatin α-chloride were synthesized and the dyes were discussed with relevance to the "H-chromophore" or "cross-conjugated chromophore". The colour-changed preperties of the dyes were also investigated by means of visible adsorption spetroscope. The novel dyes from isatin α-chloride are of theoretical interest and such dyes can be used as continuous pH indicators in acid/base titrimetric analyses or redox indicator in their specific behaviour.