The rolling of metal sheet often leads to strong contamination of the resulting surface.The present work reports the effects of the surface contamination remaining after rolling of AZ31 Mg alloy on plasma electrolytic oxidation (PEO) treatment of the resulting sheet material.Results indicate that most of the contaminants on the surface of as-rolled AZ31 Mg alloy are removed in the early stages of PEO process.The contaminations slightly influence the phase composition of PEO coating.Non-uniform distribution of contaminations results in aggregation of pores on the surface of PEO samples.On the bare substrate the contaminations are responsible for poor wear and corrosion resistance but final PEO coatings reveals similar performance on contaminated substrate compared to the abraded one.A self-cleaning property of the PEO and possibility of one step process,avoiding pre-cleaning stages,is suggested.