In this research, optical observations, X- ray diffraction and hardness measurements were used to monitor the effects of yttrium (Y) additions on as cast ZRE1 magnesium alloy. 0.75 wt.% Y was added and compared with the base alloy. The microstructure results show the refinement of the grain by the addition of Y and the grains became smaller about 32 %, which led to the increment of hardness from 50 HV (as-cast ZRE1) to 56.6 HV (as-cast ZRE1+0.75 Y). EDS results showed that the base alloy mainly contained α-Mg matrix and  Mg-Zn-Ce as a second phase crystallized along the grain boundaries and with the addition of Y, Mg-Zn-Y-Ce phase was found as a new second phase, where Y combined with the original second phase.