Friction stir processing (FSP) is a material processing technique recognized to enhance the mechanical properties of the material owing to micro-structural refinement. In the present study, the feasibility of the use of FSP for processing of mild steel has been explored. Using FSP, the micro-structural refinement of the steel surface was obtained, resulting in an average grain sizes of the order of 100 nm as confirmed by atomic force microscopy (AFM). Along with grain size refinement, an evolution of various phases was also studied with the help of X-ray diffraction (XRD). It was observed that ferrite was the only phase present in both processed and unprocessed steel.FSP was found to be useful to enhance the micro-hardness of the steel by 50 to 80%, in comparison with that of the un-processed steel. © (2013) Trans Tech Publications, Switzerland.