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　°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.　©　2017　American　Chemical　Society.