In this paper, the effects of Ce, Sn and Gd additions on the as-cast microstructure and mechanical properties of Mg-3.8Zn-2.2Ca (wt%) magnesium alloy are investigated and compared. The results indicate that adding 1.0 wt% Ce, 1.0 wt% Sn or 1.0 wt% Gd can effectively refine the grains of the Mg-3.8Zn-2.2Ca alloy, and the refinement efficiency of Ce addition is relatively high, followed by the additions of Sn and Gd, respectively. Accordingly, the tensile properties of the as-cast Mg-3.8Zn-2.2Ca alloy are improved by the additions of Ce, Sn or Gd, with the improvement resulting from the Ce addition being best and followed by the additions of Sn and Gd, respectively. In addition, adding 1.0 wt% Ce, 1.0 wt% Sn or 1.0 wt% Gd to the Mg-3.8Zn-2.2Ca alloy can also improve the creep properties of the as-cast alloy. Among the Ce-, Sn- and Gd-containing alloys, the creep properties of the Sn- and Gd-containing alloys are similar but lower than that of the Ce-containing alloy.