Exploring pH-insuspensible catalysts for pollutant treatments is still a challenge because of the pH-dependent catalyst stability. A recently developed manganese complex, Mn(Me2EBC)Cl-2, (Me2EBC; 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.62]hexadecane) was investigated to decolorize dyes in the pH range of 1-13 using H2O2 as the oxidant, and its stability in service was examined by periodically adding fresh dye and oxidant The results display that this manganese complex is capable of decoloring dye in both acid and base and keeping activity for a long service period. In addition, its modified analogue, Mn(Et2EBC)Cl-2, can perform efficient decolorization in the whole pH range from pH 1 to 13. Combinatorial methods including stoichiometric treatments of dye with freshly synthetic manganese(IV) complex, utilization of radical scavenger, and intermediate analysis by UV-visible spectrophotometry were applied for its mechanistic Studies, and a manganese(IV) hydroperoxide intermediate has been suspected to serve as the key active species in decolorization.