A composite material based on the WE43 magnesium alloy and containing nano-sized hardystonite ceramic particles was processed by means of friction stir processing (FSP). Compressive strength and strain-at-failure of the WE43 alloy increased as a combined result of FSP and nanoparticle reinforcement. The results of potentiondynamic polarization and electrochemical impedance spectroscopy tests indicated that the corrosion mechanism of the nanocomposite is combination of uniform corrosion and localized pitting corrosion which is not different from the base metal. However, the corrosion rate is significantly decreased as a result of reduced localized corrosion of the base metal after FSP and the effect of hardystonite to reduce pitting corrosion. The polarization resistance is increased from 192.48 to 339.61 and 1318.12 Ω/cm2 by applying FSP on WE43 and addition of nano-sized hardystonite particles, respectively. Indeed, the fabricated nanocomposite shows significantly increased corrosion resistance. Enhanced strength, ductility and corrosion resistance were attributed to grain refinement in addition to the fragmentation and redistribution of second-phase particles in the magnesium matrix, occurring during FSP.@en