In this work, the high performance as-cast low RE (rare earths) Mg96.5Zn1Y1.5Mn1 alloys with LPSO (long-periodic stacking ordered) phase were fabricated by Ni and Bi microalloying, and the influences of Ni and Bi additions on microstructural evolution and mechanical properties in as-cast Mg96.5Zn1Y1.5Mn1 alloy were investigated. Results show that the Ni and Bi co-alloying can greatly refine the microstructure and facilitate the precipitation of 18R-LPSO phase. Meanwhile, in the Mg95.9Zn1Y1.5Mn1Ni0.5Bi0.1 alloy, the nucleation and growth ability of 18R-LPSO phase were higher than those of W phase, and the growth pattern of 18R-LPSO and W phase was optimized from coupled to divorced growth. Besides, the Mg95.9Zn1Y1.5Mn1Ni0.5Bi0.1 alloy exhibited superior mechanical properties with yield strength (YS), ultimate tensile strength (UTS) and elongation (EL) of 167±1 MPa, 239±1.6 MPa and 12±0.45%. Grain refinement, continuous 18R-LPSO phase with optimized growth pattern and the LPSO fibers precipitated in W phase were responsible for the outstanding mechanical properties. •Effect of Ni/Bi on low RE Mg96.5Zn1Y1.5Mn1 alloy containing LPSO was studied.•The growth pattern transformation of 18R-LPSO and W phase was clarified.•The 18R-LPSO phase exhibited higher nucleation and growth ability than W phase.•The excellent mechanical properties were achieved via Ni and Bi co-microalloying.