A356/Al 2 O 3 surface nanocomposite was produced by friction stir processing (FSP) method. X-ray diffractometery, optical and scanning electron microscopy, microhardness and nanoindentation tests were used to characterize the samples. The results indicated that the uniform distribution of Al 2 O 3 particles in A356 matrix by FSP process can improve the mechanical properties of specimens. The hardness and elastic modulus of the as-received A356, the sample treated by the FSP without Al 2 O 3 particles, surface micro- and nanocomposite specimens were about 75Hv and 74GPa, 69Hv and 73GPa, 90Hv and 81GPa, 110Hv and 86GPa, respectively.