Abstract: As-cast Mg-4Zn-4Y alloy was treated by homogenization annealing at different temperatures (440,460,480℃) for different holding times (4-24 h), and the effects of homogenization annealing on the microstructure and properties of the alloy were studied. The results show that there were α-Mg phase, W phase Mg₃Zn₃Y₂, LPSO phase Mg₁₂ZnY and yttrium-rich phase in the as-cast alloy. With increasing annealing temperature, most of the LPSO phase gradually dissolved into the matrix. With increasing annealing temperature and holding time, the content of yttrium-rich phase decreased, and the dendrite segregation was reduced. Compared with the as-cast alloy, the tensile strength of the alloy after homogenization annealing at 440℃ and 460℃ decreased slightly, and the percentage elongation after fracture changed slightly. The tensile strength and percentage elongation after fracture after homogenization annealing at 480℃ were relatively high, but the burning loss occurred. The best homogenization annealing of the alloy was 440℃×12 h.