The microstructures, mechanical properties, biodegradation behavior, and cytocompatibility of the as-cast Mg-2Ga and Mg-5Ga alloys were investigated. The microstructure characteristics were studied by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The results show that the Mg₅Ga₂ precipitates with globular and strip-like shapes are formed along the grain boundaries in Mg matrix after Ga addition. The grains of Mg-Ga alloys are obviously refined by Ga addition. The tensile tests reveal that the mechanical properties of Mg-Ga alloys are enhanced by Ga addition via solution strengthening, grain boundary strengthening, and precipitation strengthening. The electrochemistry and immersion corrosion tests in simulated body fluid at 37 °C reveal that the improved corrosion behavior is attributed to the enhanced surface stability caused by Ga addition of low content. In addition, the indirect contact assay suggests that both Mg-2Ga and Mg-5Ga alloys exhibit favorable cytocompatibility with no cytotoxicity for the mouse fibroblast (L929) cells.