Magnesium-based alloys have attracted great interest for medical applications due to their unique biodegradable capability and desirable mechanical properties. When considered for medical applications, the degradation rate of these alloys must be tailored so that: (i) it does not exceed the rate at which the degradation products can be excreted from the body, and (ii) it is slow enough so that the load bearing properties of the implant are not jeopardized and do not conflict prior to and during synthesis of new tissue. Implant integration with surrounding cells and tissues and mechanical stability are critical aspects for clinical success. This study investigated Magnesium-Zinc-Strontium (ZSr41) alloy degradation rates and the interaction of the degradation products with human embryonic stem cells (hESC) over a 72 hour period. An in vitro hESC model was chosen due to the higher sensitivity of ESCs to known toxicants which allows to potentially detect toxicological effects of new biomaterials at an early stage. Four distinct ZSr41 compositions (0.15 wt.%, 0.5 wt.%, 1 wt.%, and 1.5 wt.% Sr) were designed and produced through metallurgical processing. ZSr41 alloy mechanical properties, degradation, and cytocompatibility were investigated and compared to pure polished Magnesium (Mg). Mechanical properties evaluated included hardness, ultimate tensile strength, and elongation to failure. Degradation was characterized by measuring total weight loss of samples and pH change in the cell culture media. Cytocompatibility was studied by comparing fluorescence and phase contrast images of hESCs after co-culture with Mg alloys. Results indicated that the Mg-Zn-Sr alloy with 0.15 wt.% Sr improved cytocompatibility and provided slower degradation as compared with pure Mg.