LAUSR

All‐inorganic lead halide perovskite (CsPbX3, X = Cl, Br, I, or their mixture) nanocrystals (NCs) have recently emerged as a promising photoelectric material; however, developing highly stable CsPbX3 NCs still remains a challenge due to their intrinsic ionic nature. This work presents a simple and facile post‐treatment strategy to encapsulate CsPbX3 NC with PbSO4 nanoshell at single‐particle level. Compared to pristine CsPbX3 NCs, the as‐prepared CsPbX3/PbSO4 NCs exhibit significant enhancement in the optical properties. Benefiting from the efficient protection of inert PbSO4 nanoshell, the obtained CsPbX3/PbSO4 core/shell NCs demonstrate great stability against polar solvents, including ethanol and acetone, and light irradiation. Furthermore, anion‐exchange reaction is strongly restricted upon the encapsulation of PbSO4 shell. This work provides an alternative approach for the synthesis of highly stable CsPbX3 NCs, and paves a new way for the preparation of core/shell heterostructures based on lead halide perovskite NCs.