The nature of the rhenium species present in the Re2O7/Al2O3 metathesis catalysts was investigated by chemical extraction and leaching using various organic salt solutions and water. By means of organic salt solutions, rhenium is extracted as perrhenate salts, and by means of water, rhenium and aluminium are extracted together with a (Re/Al) molar ratio of 3. This result is a first indication for the presence of Al(ReO4)(3) (or a decomposition product of Al(ReO4)(3)) in Re2O7/Al2O3 catalysts. Furthermore, using IR spectroscopy, we pointed out a approximate to 1320 cm(-1) band characteristic of ammonia coordinated on aluminium perrhenate which corroborates our results. We showed that aluminium perrhenate mixed with silica is active in the metathesis reaction.