Magnesium and its alloys have been widely studied as biomaterials for over a decade due to their good biocompatibility, good bio-mechanical properties and biodegradation in human body. However, most of them are commercial magnesium alloys, which are not taken biocompatibility into account. Even though some novel magnesium alloys were developed recently, there are still no biodegradable magnesium alloys available for clinical application because of the rapid corrosion rate and localized corrosion mechanism. In order to develop new kinds of biodegradable magnesium alloys with excellent mechanical properties and corrosion resistance in simulated body fluid, four alloys with nominal composition Mg-(4-x)Nd-xGd-0.3Sr-0.2Zn-0.4Zr (mass fraction, %, x=0, 1, 2, 3) were prepared by gravity casting on the basis of previous studied Mg-Nd-Zn-Zr alloys, and solution treatment + artificial aging treatment (T6) was conducted on the as-cast alloys. The phases were identified using XRD, the microstructure was observed with SEM, the tensile properties and microhardness were carried out using tensile test machine and microhardness tester, the corrosion rate of the alloys was evaluated in simulated body fluid by mass loss method, and corrosion morphology was observed by SEM. It was found that Mg₄₁Nd₅ phase was formed in grain boundaries when Gd addition was less than Nd, while Mg₃Gd was formed when Gd addition was more than Nd. The microstructure was refined firstly but was coarsen finally, and the volume fraction of the second phase decreased with increasing Gd addition due to relatively large solubility of Gd in Mg matrix than Nd. The mechanical properties at room temperature and corrosion resistance of the as-cast alloys at 37.5 ℃ were improved with Gd addition. As for the T6 state alloys, the strength and microhardness of the alloys with Gd addition were lower than those of the alloy without Gd, which indicates that the precipitation strengthening effect of Gd is weaker than that of Nd. Nevertheless, the corrosion resistance of the alloys with Gd addition was better than the alloy without Gd under T6 condition. The four alloys both under as-cast and T6 conditions exhibit relatively uniform corrosion mode, which is a desired corrosion characterization for degradable biomaterial.