Oxidative dehydrogenation of ethane and isobutane was investigated using chromium-vanadium-niobium mixed oxide catalysts with different compositions (Cr0.63V0.27Nb0.1, Cr0.67V0.24Nb0.09, Cr0.71V0.21Nb0.08, Cr0.74V0.19Nb0.07, Cr0.78V0.16Nb0.06). In the oxidative dehydrogenation of isobutane to isobutylene, selectivity and yield values reaching to 0.9 and 0.4, respectively, were obtained at a fractional conversion level of 0.45 with Cr0.74V0.19N0.07 catalyst at 573 degreesC. Decrease of chromium content of the catalyst caused a decrease in both selectivity and activity. CH, formation was found to cause a decrease in ethylene selectivity in the oxidative dehydrogenation of ethane. At 570 degreesC and with an O-2/C2H6 feed ratio of 0.5, ethylene and methane selectivity values of about 0.2 and 0.5 were obtained, respectively, at a conversion level of 0.3 over Cr0.74V0.19Nb0.07 catalyst. DRIFTS studies carried out at reaction conditions indicated the presence of OH stretchings and ethyl, vinyl and formyl species on the surface in the oxidative dehydrogenation of ethane. Following the DRIFTS results, reaction mechanisms were proposed for the oxidative dehydrogenation of ethane and isobutane.