The behaviors of VOx/AlMCM-41 on the oxydehydrogenation of ethylbenzene into styrene in the presence of CO2 were examined, and VOx/AlMCM-41 was characterized by XRD, N-2 adsorption-desorption isotherms, UV-Raman spectra and H-2-TPR. The maximum styrene yield 50.6% and high styrene selectivity 96.7% were obtained over 1.0 mmol/g VOx/AlMCM-41, which suggested that the isolated and polymeric VOx species were responsible for the high activity. Styrene yield and selectivity in the presence of CO2 were higher than that in the presence of N-2 because CO2 can resume the oxidative state of reduced vanadium.