The oxidative dehydrogenation of ethane into ethylene by CO2 over a series of silica-supported chromium oxide catalysts was investigated. The results showed that the catalysts were effective for the reaction and CO2 in the feed promoted the catalytic activity. The 5%Cf/SiO2 catalyst exhibited the excellent performance with 30.7% ethane conversion and 96.5% ethylene selectivity at 700degreesC. ESR and UV-DRS were used to probe the active sites and the species with high valent states (Cr5+ and/or Cr6+) were found to be important for the reaction.