Surface grain refinement is a relatively new process aimed to enhance mechanical material properties. In this study Al7075-T6 bars have been shot peened with parameters much different from those of conventional shot peening. Microstructure gradient has been observed by means of transmission electron microscopy (TEM), X-ray diffraction (XRD) and nano indentation tester. A fine grained layer was found on top surface of the specimens. Measurements indicate of notable improvements in cases of hardness and elastic modulus in comparison with untreated material. XRD results also show significant depth affected both in terms of residual stress and FWHM. The results imply that using optimized shot peening parameters, it would be possible to create a fine grained layer on surface of component and consequently increase fatigue life and any other property affected by grain size.