A facile synthesis of green-emitting all-inorganic (CsPbBr 3 ) and organometallic [methylammonium (MA)PbBr 3 and formamidinium (FA)PbBr 3 ] perovskite nanocrystals (NCs) with near-unity photoluminescence quantum yields, narrow emission bandwidths (fwhm < 22 nm), and much improved colloidal stability has been reported here. A low-cost and highly reactive bromide precursor 1,3-dibromo-5,5-dimethylhydantoin was employed in our synthesis that not only rendered excellent stability to all three NCs (Cs/MA/FAPbBr 3 ) but also eased the synthesis of high-quality MAPbBr 3 NCs even at moderate temperatures. At high temperatures, MAPbBr 3 NCs decompose by releasing gaseous methylamine, making their synthesis a difficult task in conventional high-temperature hot injection method. Our synthesized NCs are coveted materials exemplified by their narrow particle size distributions, excellent colloidal stability in ambient conditions, and high tolerance toward UV light and polar solvents. All these astonishing properties signify their better suitability in real applications like displays, low-threshold lasers, and light-emitting diodes.