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The oxidative dehydrogenation of isobutane over SiO2-supported and unsupported NiMoO4 was studied under steady state conditions and the effect of active phase loading analysed.The SiO2-supported catalysts were prepared by direct precipitation of NiMoO4 on the support and characterised by BET, X-ray diffraction and temperature-programmed desorption of NH3. Used catalysts were characterised by thermal analysis. Results show that, in SiO2-supported catalysts, β-NiMoO4 is stabilised even at room temperature. The SiO2-supported NiMoO4 catalyst with lower contents of active phase (13% NiMoO4/SiO2 and 26% NiMoO4/SiO2) present higher amount of β phase and less acidic surfaces.Besides isobutene, the reaction of isobutane over the prepared catalysts leads to the formation of CO2, CO, light alkanes and coke. Unsupported NiMoO4 leads to much higher amounts of total oxidation products and coke than the supported catalysts. The catalyst containing the highest amounts of β-phase (26% NiMoO4/SiO2) leads to higher selectivity to isobutene. [Copyright &y& Elsevier]