Creating highly stable inorganic perovskite nanocrystals (CsPbX3, where X = Cl, Br, and I) with excellent optical performance is challenging because their optical properties depend on their ionic structure and its inherent defects. Here, we present a facile and effective synthesis using a nanoconfinement strategy to grow Mn2+-doped CsPbCl3 nanocrystals embedded in dendritic mesoporous silica nanospheres (MSNs). The resulting nanocomposite is abbreviated as Cs(Pb x/Mn1- x)Cl3@MSNs and can serve as the orange emitter for white light-emitting diodes (WLEDs). The MSN matrix was prepared via a templated sol-gel technique as monodispersed center-radial dendritic porous particles, with a diamater of ∼105 nm and an inner pore size of ∼13 nm. The MSN was then utilized as the matrix to initiate the growth of Mn-doped perovskite nanocrystals (NCs). The NCs in the resulting composite have an average diameter of 8 nm and a photoluminescence quantum yield of >30%. In addition, the optical properties of the Cs(Pb x/Mn1- x)Cl3@MSNs can be tuned by varying the Mn2+ doping level. The resulting composites presented a significantly improved resistance to ultraviolet (UV) light, temperature, and moisture compared to that of bare Cs(Pb0.72/Mn0.28)Cl3. Finally, we fabricated down-converting WLEDs by using Cs(Pb x/Mn1- x)Cl3@MSNs as the orange-emitting phosphor deposited onto UV-emitting chips, demonstrating their promising applications in solid-state lighting. This work provides a valuable approach to fabricating stable orange luminophores as replacements for traditional emitters in light-emitting diode devices.