The colloidal-atomic layer deposition (c-ALD) method is employed to grow a zinc sulfide (ZnS) shell on CsPbBr perovskite quantum dots (PeQDs) to form CsPbBr/ZnS core/shell heterostructures to address the intrinsic stability challenges of PeQDs. The c-ALD process offers layer by layer control over the thickness of the shell, enabling uniform and conformal encapsulation, which significantly passivates the surface defects and enhances the optical properties of the PeQDs. This approach significantly improves photoluminescence quantum yield, increases environmental stability, and prolongs the average radiative lifetime of the CsPbBr PeQDs. The structural and spectroscopic analysis confirms the formation of a thick and uniform ZnS shell. Furthermore, the resulting core/shell PeQDs exhibit exceptional thermal, photostability, and aqueous durability, surpassing the limitations of pristine CsPbBr PeQDs. This work opens new opportunities for the c-ALD method to be integrated into perovskite core/shell heterostructures for advancing optoelectronic technologies.