Although the anodising process has been widely used in surface treatment of Al alloys, the well known sulphuric acid anodising process produces inhomogeneous and highly porous anodised coatings on Al alloys containing high Si due to the inertness of the silicon particles. The present work reports a novel micro-arc anodising process for such high-silicon aluminium alloys. Uniform and thick anodising coatings can be obtained through an anodising process in an alkaline electrolyte under high voltage and low current density conditions. The microstructure examination in SEM indicates that most pores in the coatings have been sealed during the anodising process, thus post-treatment that is normally needed for the currently used anodising process can be eliminated. The coating is very promising in the improvement of corrosion resistance for cast high-silicon aluminium alloys.