The effect of second phases on the creep behavior of Mg-Ca-Zr alloys was investigated. Casting and hot-extrusion processes were performed to prepare Mg-xCa-0.5Zr (x = 0 wt.%, 0.3 wt.% and 0.6 wt.%) alloys with different morphologies and distributions of second phases. The as-cast microstructures of Mg-Ca-Zr alloys consisted of an Mg matrix and coarse Mg₂Ca intermetallic compounds distributed at the grain boundaries. The hot-extruded microstructures exhibited finer Mg₂Ca spherical particles and precipitates distributed homogeneously inside the matrix and along the grain boundaries. The results of creep tests suggested that the viscous glide of dislocation and dislocation climb were the dominant creep mechanisms of Mg-Ca-Zr alloys crept at 200°C. The creep property was strongly related to the morphology and distribution of the Mg₂Ca phases. The finer and more homogeneously distributed particles showed a better strengthening effect than the coarser intermetallic compounds distributed along the grain boundaries.