<p>In this paper, the effect of Gd content on the high temperature creep behaviors of as-cast Mg-xGd-0.4Zr (x = 1, 5, 10 wt.%) alloys was investigated. The results showed that the as-cast Mg-10Gd-0.4Zr alloy had the highest tensile strength, while the as-cast Mg-5Gd-0.4Zr alloy had the best elongation. The creep properties of the as-cast Mg-xGd-0.4Zr alloy increased gradually with increasing the Gd content, which was accompanied with the transformation of creep mechanism. For the as-cast Mg-1Gd-0.4Zr alloy dislocation slip, dislocation cross-slip and a high amount of twins dominated the steady-state creep process due to the low strength. When the Gd content increased to 5 wt.%, dislocation slip played major role. Simultaneously, the number of twins decreased and some pyramidal &lt; c + a &gt; dislocations were observed, which can be ascribed to the increased solid solution strengthening and a small amount of dynamic precipitates. For the as-cast Mg-10Gd-0.4Zr alloy, the creep mechanism transformed into dislocation climb as well as more activated pyramidal &lt; c + a &gt; dislocations. In addition, the twin was absolutely suppressed, and the dynamic precipitates became denser during creep testing, which can well account for the best creep performance of the as-cast Mg-10Gd-0.4Zr alloy.</p>