The aim of this work was to investigate the catalytic performance of the AZrO(3) (A: Ca, Sr or Ba) catalysts for the dehydrogenation of ethylbenzene (EBDH) to produce styrene and to clarify an important factor for the high dehydrogenation activity. Among the AZrO(3) catalysts, only the BaZrO3 (BZO) catalyst showed a significantly high activity for EBDH and the activity increased with time, while the CaZrO3 and SrZrO3 catalysts almost did not provide any activity at 823 K. Comparing the styrene yield over the BZO catalyst with that over the industrial potassium-promoted iron oxide (Fe-K) catalyst, the BZO catalyst showed a lower styrene yield than the Fe-K catalyst at the initial stage of the reaction. However, after 40 min of EBDH, the BZO catalyst exhibited a higher styrene yield than the Fe-K catalyst. Based on an ESR measurement, a sharp signal at g = 2.004, which was identified as an unpaired electron trapped in oxygen vacancies, was detected in the BZO catalyst after dehydrogenation. The number of oxygen vacancies increased with change in the dehydrogenation activity. In addition, the BZO catalyst with a pretreatment by H-2 reduction presented a high activity without an induction period. Comparing the profiles of the temperature desorption of ethylbenzene (EB) over the prereduced catalyst to that of the untreated BZO catalyst, a chemisorbed species of EB was detected over the prereduced BZO catalyst, although a physisorbed species was present on the surface of the untreated catalyst. Hence, the production of oxygen vacancies opened the adsorption channel of EB and created the reactive site, which produced a high EBDH activity. (C) 2014 Elsevier B.V. All rights reserved.