Abstract: The composition of as-cast Mg₈₅Zn₆Y₉ alloy with almost 100% long period stacking ordered structure (LPSO) phase was milled into nanocrystalline powder by the high energy ball milling, then was mechanical blended with atomized Mg-9Al-1Zn(AZ91) powder. The Mg₈₅Zn₆Y₉/AZ91 composites with the mass fraction of Mg₈₅Zn₆Y₉ powder from 0wt% to 30wt% were prepared by spark plasma sintering (SPS) at 350℃. The microstructure of Mg₈₅Zn₆Y₉/AZ91 composites was characterized with optical microscope (OM), SEM and TEM; XRD was used to analyze phase transition of the composite before and after solid solution treatment; microhardness and compression test were also carried out to study the mechanical properties of the composites. The results show that the Mg₈₅Zn₆Y₉ powder's grain size decreases and the microhardness of the Mg₈₅Zn₆Y₉ powder increases obviously after 3 h high energy ball milling. In addition, the Mg₈₅Zn₆Y₉ powder is mainly distributed at the boundaries of the AZ91 matrix powder. With more addition of Mg₈₅Zn₆Y₉ powder, the Mg₈₅Zn₆Y₉ powders likely combine with each other to form a continuous grid. Moreover, there is no obvious transition layer at the interface between Mg₈₅Zn₆Y₉ powder and matrix. After solid solution treatment at 400℃ for 24 h, β phase is dissolved into the matrix and LPSO phase is disappeared gradually. The compressive yield strength at room temperature of the prepared 20wt% Mg₈₅Zn₆Y₉/AZ91 composite with best performance changes from 200 MPa to 230 MPa, which the yield strength is significantly enhanced compared with AZ91 without Mg₈₅Zn₆Y₉ powder addition.