Cs₄PbBr₆ nanocrystals (NCs) have been recently studied as they can enhance the light emitting efficiency and stability of CsPbBr₃ NCs. However, the synthesis of Cs₄PbBr₆ NCs is often accompanied by the generation of CsPbBr₃ NCs, and less attention has been paid to how to exactly control their formation. Here, we investigated the key factors in deciding the final products in the hot-injection synthesis by a modified amine-free method. We found that the molarity ratio of Cs/Pb dominated the final products, while the amount of bromine had a relatively small effect. In addition, introducing a certain amount of oleylamine into the amine-free reaction leads to the formation of Cs₄PbBr₆, instead of CsPbBr₃ NCs. This clearly shows that the protection ligand oleylamine also plays an important role in the formation of Cs₄PbBr₆ NCs. This well understood and fine control of the synthesis may inspire a new CsPbBr₃@Cs₄PbBr₆ core–shell structure, with the same chemical elements but a different crystal phase in the core and the shell. This nanostructure would open a new avenue for enhancing the stability of perovskite nanocrystals.