Abstract: Fe_0.6Cr_0.4/Bi₇MnO_12.5 composite nanoparticles were prepared by chemical precipitation method and the materials were characterized by XRD TEM and FTIR. The resulting composite nanoparticles were impregnated with the solutions of Na₂CO₃ and K₂CO₃ and used to promote the photocatalytic degradation of blue dyestuffs. It has been found that the composite nanoparticles have an average size of 24.0 nm. The nanoparticles impregnated with the solutions of Na₂CO₃ and K₂CO₃ speed up the photocatalytic degradation of various blue dyestuffs greatly and thus can be used for the wastewater treatment containing the blue dyestuffs.