<p>Magnesium alloys are lightweight high-performance alloys. However, they are limited in practical engineering applications due to their susceptibility to tearing and insufficient filling ability during the casting process. In this study, the influence of rare earth element La on the hot tearing susceptibility and fluidity of AZ80 magnesium alloy was investigated using a hot tearing test and a fluidity test. The results show that with the addition of La, the hot tearing susceptibility of AZ80 magnesium alloy first decreases and then increases, while the casting fluidity first increases and then decreases. The addition of La changes the quantity and morphology of the eutectic phase. The addition of an appropriate amount of La increases the content of Mg₁₇Al₁₂ that effectively participates in feeding during the late stage of solidification. Meanwhile, the formed Al₁₁La₃ rare earth phase can act as a heterogeneous nucleation core to reduce the grain size and increase the grain boundary area, thereby inhibiting the propagation of hot tears. In addition, the addition of La increases the residence time of the liquid phase during the solidification process and weakens the hindrance of the eutectic phase to the liquid flow, thus increasing the fluidity.</p>