Nanocrystalline Ni and Ni alloys (Ni-Fe and Ni-P) have been prepared using electrodeposition in nickel sulphate based baths. The deposits were characterised by several methods, in particular three-dimensional atom probe (3DAP) analysis. The 3DAP technique makes it possible to perform chemical analysis on a near-atomic scale, which is essential for the studies of nanocrystalline materials. The impurity levels in the as-deposited materials were found to be low, typically less than 0.3 at.%, showing no significant enrichment at grain boundaries. After heat treatment however, grain boundary segregation of impurities has been observed.