<p>The effects of alloying elements (Al and Zn) on the second-phase transformation and deformation mechanisms were revealed using the microstructure characteristics, and the mechanical behaviour of Mg–4Y–(4 − <i>x</i>)Al–<i>x</i>Zn was systematically investigated. The results showed that the Al‒Y phase (Al₂Y and Al₁₁Y₃) was formed in the Mg‒4Y‒4Al alloy. When both Al and Zn were contained, the AlZnY phase was produced, and correspondingly, as the Al–Y phase decreases. In addition, as the Zn content exceeded 2 wt%, the W phase was formed in the alloy system. In the alloy under investigation, the axial ratio (<i>c/a</i>) of α-Mg was lower than that of pure Mg. These results indicated a reduction in the disparity between the slip systems along the <i>a</i>-axis and <i>c</i>-axis directions. The yield strength and ultimate tensile strength initially decreased and then increased as the Zn content increased. Additionally, the elongation decreased with the incorporation of Zn, and the Mg–4Y–4Al formulation exhibited the highest ductility at 11.6%. The primary mechanism contributing to the strengthening of Mg–4Y–(4 − <i>x</i>)Al–<i>x</i>Zn was the influence of second-phase strengthening and solid-solution strengthening.</p>