A novel optimization approach is proposed to extract mechanical properties of a power law material from its given experimental nano-indentation P-h curves. A set of equations have been established to relate the P-h curve to mechanical properties, E, σ y and n, of a material. Using the proposed optimization approach, convergence studies were carried out for the determination of the mechanical properties of materials. It was found that the mechanical properties of an elastic-plastic material usually cannot be uniquely determined using a single loading and unloading P-h curve. Thus a technique has also been developed to determine the material properties from indentation p-h curves using indenters with two different angles. This enables the mechanical properties of materials to be uniquely determined.