Printing and dyeing wastewater (PDW) decolorization by natural cryptomelane was studied in aqueous and acidified suspensions on the basis of the oxidation and deoxidization property of natural cryptomelane. The results show that the reaction rate increases with the decrease of pH and grain size and the increase of mineral quantity and time,and the addition of sodium nitrate is in favor of the decolorization of dyes whereas the phosphate inhibits the reaction. 10 kinds of PDW were treated in the experiment, the decolorization rate of most of dyes can be up to 95%, with the lowest one above 84%. The PDW of Huafeng Plant after treatment reaches level I discharge criterion of industrial wastewater. Based on the experiment on solubility of natural cryptomelane, Mn(Ⅳ) can be deoxidized into Mn(Ⅱ), it is tentatively proposed that the possible reaction scheme is the xidation-deoxidization reaction.