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As-extruded Mg-Sr alloy,a kind of promising biodegradable biomedical material,was coated using micro-arc oxidation and also using a phosphate conversion coating.The corrosion behaviors were investigated using Hanks\' solution.The corrosion of the as-extruded Mg-Sr alloy became more serious with increasing immersion time;that is,the corrosion pits became more numerous,larger and deeper.The micro-arc oxidation coating and the phosphate conversion coating were effective in improving the corrosion resistance of the as-extruded Mg-Sr alloy.The micro-arc oxidation coating was much more effective.Moreover,the as-extruded Mg-Sr alloy and the coated as-extruded Mg-Sr alloy exhibited lower corrosion rates than the as-cast Mg-Sr alloy and the corresponding coated as-cast Mg-Sr alloy,indicating that the corrosion properties of the coated samples are dependent on their substrates.The finer microstructure of the substrate of the as-extruded condition corroded much slower.The corrosion resistance of the coated Mg-Sr alloy depended on the coating itself and on the microstructure of the substrate.