Magnesium alloys attracted more and more attentions as biodegradable implant materials because of their properties similar to cortical bone. From the perspective of element biosafety and dietetics, the ideal alloying elements suitable for biodegradable applications should be those essential to or naturally presented in the human body. This study presents a novel aluminum-free magnesium alloy system with Si selected as a major alloying element, due to its superior biocompatibility in biological environment, especially in bone regeneration and repairment. Mg–Si binary alloys with different Si contents were prepared in a permanent mould via gravity casting and direct-chill casting. The microstructures, corrosion properties and mechanical properties were inves- tigated as a function of alloy composition.