The effect of Ce content (0–1.6 wt.%) on the modification of Mg₂Si phase in the as-cast Mg-5Al-2Si alloy was investigated. The original Chinese script type Mg₂Si phase was refined distinctly and transformed to dispersive block shape gradually by adding Ce element. The length of Chinese script type Mg₂Si phase was reduced from 110 to 50 µm with increasing Ce content to 1.6 wt.%. The results calculated by Pandat software indicated that the added Ce element first combined with Si to form CeSi₂ phase, which could serve as the heterogeneous nucleation of Mg₂Si phase due to the small lattice mismatch of 7.97%. The modification of Mg₂Si phase was mainly attributed to the facts that Ce changed the growth steps of Mg₂Si phase and CeSi₂ promoted the nucleation of Mg₂Si phase. With increasing Ce content from 0 wt.% to 1.6 wt.%, the YS, UTS and EL at 150 ℃ were improved from 67.7 MPa, 91.2 MPa and 1.6% to 84.2 MPa, 128 MPa and 7.5%, respectively.