The dehydrogenation of isobutane in the presence of CO2 over NiO supported on gamma-Al2O3 was investigated. For comparison, CIA supported on gamma-Al2O3 was also investigated. Conventionally, catalysts used for the dehydrogenation of various alkanes suffer catalyst deactivation due to carbon deposition. In the present study, the yield of isobutene was significantly decreased with time-on-stream due to carbon deposition using Cr2O3(x)/gamma-Al2O3, where x indicates the loading of a corresponding oxide by weight %. Carbon deposits were also evident on NiO(x)/gamma-Al2O3; however, the yield of isobutene was enhanced with time-on-stream depending on the loading (x). This indicates that the contribution of the carbon deposition in the dehydrogenation on NiO(x)/gamma-Al2O3 definitely differed from that on an ordinary catalyst system, such as Cr2O3(x)/gamma-Al2O3. To confirm the advantageous effect of carbon deposition exerted on the yield of isobutene, NiO(x)/gamma-Al2O3 was first treated with isobutane, following which its catalytic activity was examined. Predictably, it became clear that the carbon deposition during the pretreatment contributed to the enhancement of the isobutene yield. The presence of an Ni-carbide species together with the metallic Ni that was converted from NiO during the dehydrogenation definitely enhanced the yield of isobutene. Although carbon deposition is generally recognized as the main cause of catalyst deactivation, the results of the present study reveal that this is not necessarily the case.