All-inorganic cesium lead halide perovskite (CsPbX3, X = Cl, Br, and I) quantum dots (QDs), possessing high photoluminescence quantum yields and tunable color output, have recently been endowed great promise for high-performance solar cells and light-emitting diodes (LEDs). Although moisture stability has been greatly improved through separating QDs with a SiO2 shell, the practical applications of CsPbX3 QDs are severely restricted by their poor thermal stability, which is associated with the intrinsically low formation energies of perovskite lattices. In this regard, enhancing the formation energies of perovskite lattices of CsPbX3 QDs holds great promise in getting to the root of their poor thermal stability, which hitherto remains untouched. Herein, we demonstrate an effective strategy through Mn2+ substitution to fundamentally stabilize perovskite lattices of CsPbX3 QDs even at high temperatures up to 200 degrees C under ambient air conditions. We employ first-principle calculations to confirm that the significantly improved thermal stability and optical performance of CsPbX3:Mn2+ QDs arise primarily from the enhanced formation energy due to the successful doping of Mn2+ in CsPbX3 QDs. Benefiting from such an effective substitution strategy, these Mn2+-doped CsPbX3 QDs can function well as efficient light emitters toward the fabrication of high-performance perovskite LEDs.