Nickel(II) bromide is the name for the inorganic compounds with the chemical formula NiBr2(H2O)x. The value of x can be 0 for the anhydrous material, as well as 2, 3, or 6 for the three known hydrate forms. The anhydrous material is a yellow-brown solid which dissolves in water to give blue-green hexahydrate (see picture).

In chemistry, water(s) of crystallization or water(s) of hydration are water molecules that are present inside crystals. Water is often incorporated in the formation of crystals from aqueous solutions. In some contexts, water of crystallization is the total mass of water in a substance at a given temperature and is mostly present in a definite (stoichiometric) ratio. Classically, "water of crystallization" refers to water that is found in the crystalline framework of a metal complex or a salt, which is not directly bonded to the metal cation.