The present work investigates on the characterization of friction stir welded dissimilar aluminium alloys AA2024 and AA5052. Performance of commonly used tool profiles were compared against the newly developed stepped pin profile. H13 tool steel was used as friction stir tool with various pin profiles which includes cylindrical, cylindrical-threaded, squared, tapered and stepped types. Tensile and hardness studies were done to analyze mechanical behaviour. Macrographs of cylindrical and tapered pins showed minute discontinuities whereas other profiles did not. Microstructure and SEM/EDAX analysis were done to examine the metallurgical changes for every trial. The optimized process parameters of speed and feed were identified to be lOOOrpm and 40 mm/min respectively. Extensive studies revealed that sound welds were produced in the plates that were welded with new stepped pin tool.