Abstract: The electron donor properties of Pr6O11 activated at 300, 500 and 800℃ are reported from the studies on adsorption of electron acceptors of various electron affinity (7, 7, 8, 8-tetracyanoquinodimethane , 2. 3. 5. 6-tetrachloro-1, 4-benzoquin one, p-dinitrobenzene, and m-dinitrobenzcne) in three solvents (acetonitrile, 1,4-dioxan and ethyl acetate). The extent of electron transfer during adsorption is understood from magnetic measurements and ESR spectral data. The corresponding data on mixed oxides of Pr and Al are reported for various compositions. The acid / base properties of these oxides are determined using a set of Hammett indicators.