Currently available engineering magnesium alloys have several critical concerns if they are about to be used as biomaterials, particularly the concern about the toxicity of the common alloying elements such as aluminum and rare earth (RE). There is an increasing demand to develop new magnesium alloys that do not contain any toxic elements. It is also desirable, yet challenging, to develop such a material that has a controllable degradation rate in the human fluid environment. This paper presents mechanical properties, degradation, and in vitro cell attachment of a newly developed Mg-6Zn magnesium alloy. The alloy demonstrated comparable mechanical properties with typical engineering magnesium alloys. However, the bare alloy did not show an acceptable corrosion (degradation) rate. Application of a polymeric PLGA or poly(lactide-co-glycolide) coating significantly decreased the degradation rate. The results obtained from cell attachment experiments indicated that the mouse osteoblast-like MC3T3 cells could develop enhanced confluence on and interactions with the coated samples.