This study systematically investigates the unusual tensile mechanical behavior of Mg-RE solid solution (SS) alloys, exhibiting anomalous tensile strengths (ATS) and an enhanced strain-hardening rate at high temperature. Both the peak ultimate tensile strength (UTS) and tensile yield strength (TYS) values occur at 150–200 ℃, which are 12–50% higher compared to those at room temperature (RT). Meanwhile, the strain-hardening rate increases with the temperature rising from RT to 200 ℃ during the plastic deformation process. The results reveal that the formation of stacking faults (SFs) and the locking of dislocations, particularly immobile 〈c〉 partial dislocations, enhance resistance to plastic deformation, leading to higher strengths at high temperature. Furthermore, the interactivity between SFs and 〈c + a〉 dislocations intensify with rising of temperature. The presence of RE atoms in the SS plays a critical role in this unique mechanical behavior, as they preferentially occupy non-basal planes rather than basal planes, thereby reducing the stacking fault (SF) formation energy. This study provides new insights into the high-temperature strengthening mechanisms of Mg-RE based alloys, offering potential guidance for the design of advanced lightweight materials with superior mechanical properties.