The catalytic oxidative dehydrogenation of ethane was investigated in a fixed-bed tubular microreactor at 500, 550 and 600 degreesC and a space velocity of 35 027 ml g(-1) h(-1). Two kinds of V-Mg oxides catalysts containing various V/Mg atomic ratios were employed. One group of catalysts was prepared by the solid reaction between. ne powders of vanadium pentoxide and magnesium nitrate and the other ones were obtained from mesostructured V-Mg-Os. For the former catalysts, it was found that the selectivity to ethene increased and the conversion of ethane passed through a maximum with increasing V/Mg atomic ratio. For the catalysts obtained from the mesoporous materials, an optimum V/Mg atomic ratio was found, for which the conversion of ethane and the selectivity to ethene were maxima. Compared with the mixed-oxide catalysts, those obtained from the mesoporous materials exhibited much higher yields to ethene. Several new phases, such as pyro-Mg2V2O7, ortho-Mg-3(VO4)(2) and meta-MgV2O6, formed between magnesia and vanadia, were identified by XRD in the mixed V-Mg oxide catalysts; they may be responsible for the catalytic activity. In the catalysts prepared from mesoporous V-Mg-O, a V2O3 phase, which may contain highly dispersed magnesium, was identified and suggested to be responsible for the higher catalytic performance.