IR spectra were taken of NiSO4. nH2O (n = 7,6,4,1,0) and of the fully and partially deuterated analogues of theirs in the region of 4000 cm−1to 300 cm−1in tablets of KBr, in Nujol in the region of 4000 cm−1to 500 cm−1, and in suspension of 1,3-hexachlorobutadiene from 4000 to 1000 cm−1. They were interpreted in relation to the stretching and bending vibrations of the hydrate water, its symmetry, the types of H bonds in which it participates (H2O – – – H - O - H – – – OSO3and H2O - - H - O - H – – – OH2) and their energy. The latter, calculated from spectroscopic data, varies within the interval of 32 - 22 kJ/mol for NiSO4.nH2O (n = 7,6,4) and is 38.9 kJ/mol for NiSO4.H2O. Correlation has been established between the E of the H bond and d(Ni ← 0). The librational vibrations were characterized mainly by the respective composite vibrations. (νL+ δH2O). The symmetry of the SO4group has been examined and compared in the various hydrates, as well as its bidentate coordination in the monohydrate.