Several NiO-MgO samples were prepared from nickel nitrate hexahydrate and different sources of magnesia by using a NiO/MgO weight ratio of 1:1 and 4:1 and two different preparative paths. All the samples were structurally characterized using BET, XRD, SEM and TPR techniques. The results showed that the sequence of decomposition of the Ni(NO3)(2) 6H(2)O-MgO systems is similar to the sequence reported for the nickel nitrate hexahydrate without magnesia. XRD identified complete solid solutions for all the NiO-MgO systems prepared. Their BET areas were similar but their different morphologies and particle sizes mainly depended on the preparative path. Independently of the magnesia used, the NiO-MgO systems prepared by controlled decomposition of the nickel nitrate hexahydrate until Ni-3(NO3)(2)(OH)(4) was formed and which were subsequently calcined to form NiO (path B) led to very homogeneous particles of sizes around 100 nm. Path B also gave the highest degrees of NiO reduction.