The syntheses of MCM-41 (Mobil Composition of Matter No. 41) supported chromium oxide catalysts at different chromium concentrations (4-10 % by mass) were carried out hydrothermally. The aim of this study was to determine the effect of chromium concentration in the catalyst structure on the chromate types and chromium oxidation states, as well as the activity of the catalyst in the isobutane dehydrogenation reaction. Inactive alpha-Cr2O3 crystals for isobutane dehydrogenation were shown to increase in the catalyst structure as the chromium loading increased. The highest amount of Cr6+ on the catalyst surface was detected in the catalyst (H4-MCM-41) with 4 % chromium by mass. Catalytic tests (T = 600 degrees C, P = atmospheric pressure, WHSV = 26 h(-1)) were performed under fixed bed reactor conditions. The highest isobutane conversion (similar to 60 %) and selectivity (similar to 80 %) were observed on the H4-MCM-41 catalyst, which had the highest amount of Cr6+ and monochromate structures. Catalyst deactivation was not due to coke deposition but, rather, was caused by the formation of inactive alpha-Cr2O3 crystal structures.