Ni-Fe hydrotalcites with Ni/Fe molar ratios of 1, 2, 3, 6 and 10 were prepared by coprecipitation. TG-DTA results showed that the hydrotalcites decomposed in two stages, corresponding to two endothermic peaks around 200 and 300 degrees C. After calcination at 400 degrees C, the hydrotalcites were converted to NiFeO mixed oxides with high surface areas around 100 m(2)/g, which exhibited the XRD pattern of NiO only. TPR studies of the mixed oxides indicated that the reduction temperatures decreased with increasing Ni content, inconsistent with the in situ Mossbauer spectroscopic results which showed that the mixed oxide (Ni/Fe = 2) was easier to reduce than the Fe2O3 sample. Microcalorimetric adsorption of NH3 and CO2 revealed that the mixed oxide (Ni/Fe = 2) displayed intermediate acidity and basicity between those of the pure oxide NiO and Fe2O3. The mixed oxides after calcination at 800 degrees C possessed the phases of NiO and NiFe2O4 with the surface area around 15 m(2)/g, which exhibited moderate basicity with only a little weak acidity.