This work presents a new approach to preparation of Co/Mn-W3O8 nanoparticles via facile sonochemical route. Cobalt and manganese codoped tungsten oxide (W3O8) nanoparticles was studied as a photocatalyst for the removal of amaranth under solar light irradiation (lambda(max) 520 nm). The results indicated that the Co/Mn-W3O8 composite photocatalyst showed higher photocatalytic activity the single element doped and pure W3O8. Moreover, the stability of Co/Mn-W3O8 was tested using recycling experiments. It is suggested that the band gap energy difference between the Co/Mn-W3O8 and W3O8 accelerates the separation of photogenerated electron-hole pairs, dominating the enhanced photocatalytic activity.