CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (NCs) have shown great potential in numerous applications including wide color gamut display and lighting. Despite the wonderful luminescence properties, the inherent instability of these NCs hinders their use in practical situations. Herein, we report a facile aqueous-based, ligand-free method to synthesize highly stable CsPbX3 NCs using ZIF-62, a metal−organic framework, as an encapsulation matrix which effectively isolates CsPbX3 from the surrounding. We discovered that the slightly alkaline nature of ZIF62 facilitates the reaction between water and PbBr2 to form PbBr(OH), which not only passivates the surface defects of the CsPbBr3 NCs but also prevents the perovskite from decomposing or oxidizing at high temperature. Sintering of ZIF-62 can therefore be performed in air at ∼300 °C to completely seal the perovskite within the insulating matrix, resulting in CsPbBr3/ZIF-62 composites exhibiting high stability against polar solvents, heat, light, and ambient humidity. Notably, the composite can maintain its bright luminescence without noticeable degradation in water for more than 2 months. The narrow-band emission and stability of these composites led to the demonstration of white light-emitting diodes with excellent color stability. Without the need for organic solvents during NC synthesis and noble gas ambient during sintering, the strategy proposed here can potentially facilitate the cost-effective, large-scale synthesis of highly stable perovskites which show great promise in commercial applications.