Sonochemical decolourisation of two categories of dyes namely anionic Acid Red 2 and cationic Rhodamine B has been investigated using sulphate radicals activated by immobilized iron. The influence of operating variables, such as pH, persulphate dose, catalyst dose and contact time in the ultrasonication assisted decolourisation of dyes has been studied and optimized in bath type ultrasonicator. The decolourisation efficiency of bath type and horn type sonication is studied under optimized conditions. In bath type, the decolourisation efficiencies of Acid Red 2 and Rhodamine B are found to be 69% and 95% in 90 min and 15 min, whereas in horn type it is 83% and 96% in 10 min and 3 min respectively. The effect of passing aeration with bath type sonication id also studied, in which Rhodamine B is found to decolourise at a faster rate on comparing the sonication alone. Studies on the leachability and reusability of catalyst are also conducted for each process. Among the processes, horn type sonication is found to be more effective than the bath type sonication-coupled-aeration and bath type sonication.