Mg alloys attract more and more attentions for biomedical applications. Mg-Gd alloys were designed as biodegradable implant materials which combine favorable mechanical and corrosion properties. In this work, the microstructure and mechanical properties of binary Mg-2Gd, ternary Mg-2Gd-(Ag, Ca) and quaternary Mg-2Gd-2Ag-0.4Ca alloys were investigated. The alloys were prepared by permanent mould casting. The results show that the additions of Ag and Ca had significant influences on the microstructure and mechanical properties of Mg-2Gd alloy. Ag and Ca additions affect the formation of second phases. A quaternary Mg-Gd-Ag-Ca second phase was found in the quaternary alloy. Both the hardness and tensile yield strength were improved by adding Ag and Ca to 2 wt% Gd-containing alloys due to grain refinement and formation of different intermetallic phases (IMPs). Furthermore, the addition of Ag and Ca can apparently enhance the age hardening of Mg-2Gd alloy.