The catalytic behavior of two mixed-valence borates was studied in ethyl acetate oxidation in respect to their different electronic structure. The studied compounds ferroferriborate (Fe3BO5) and magnesium ferroferriborate (Fe2MgBO5) are members of a solid solution series, which allows to synthesize samples with different mixed valence ions content. A number of methods, such as XRD, ISP, krypton adsorption, XPS and Moessbauer spectroscopy are used for sample characterisation. The catalytic experiments, as well as in situ Moessbauer investigation of the studied oxides in the course of ethyl acetate oxidation are also performed. It is established that ferroferriborate having higher mixed valence cations content shows higher catalytic activity. It is observed, that electron exchange (EE) in mixed valence metal oxide catalyst provides optimal conditions for ethyl acetate total oxidation. However, in respect to the observed selectivity against by-products formation, the electron delocalization (ED) should be located in a limited range. A partial oxidation of iron ions in the studied compounds, mainly in their surface, is observed after catalytic tests. (c) 2005 Elsevier B.V. All rights reserved.