All-inorganic　CsPbX3　(X　=　Cl,　Br,　and　I)　perovskite　nanocrystals　(PeNCs)　and　nanocomposites　have　shown　great　promise　in　optoelectronics　and　photovoltaics.　However,　it　remains　notoriously　difficult　to　control　over　perovskite　nanocomposites　at　a　single　particle　level.　Herein,　we　report　a　unique　photoinduced　method　for　the　controlled　synthesis　of　CsPbX3　PeNCs　and　nanocomposites　based　on　the　light-triggered　breakage　of　the　covalent　carbon-halogen　bond　of　haloalkanes.　The　use　of　molecular　haloalkanes　as　unreactive　halide　source　provides　a　mild　reaction　condition,　which　enables　in　situ　confined　growth　of　CsPbX3　PeNCs　in　mesoporous　nanospheres　such　as　silica　with　well-defined　morphology.　As　a　result,　a　variety　of　multifunctional　perovskite　nanocomposites　can　be　achieved　through　photoinduced　confined　growth　of　PeNCs　in　mesoporous　silica　coated　nanoparticles.　These　findings　provide　a　general　approach　for　synthesizing　CsPbX3　PeNCs　and　nanocomposites,　which　may　open　up　new　opportunities　for　perovskite-based　material　or　device　engineering　towards　versatile　applications.　(C)　2021　Elsevier　Ltd.　All　rights　reserved.