We report a study on the desorption properties, crystallography and chemical state of MgH2 and 1 mol% Nb2O5 ball-milled composites. Desorption temperatures of the composites decreased with increase of ball-milling time. Size of MgH2 crystallites decreased during ball-milling. Reduction of Nb2O5 after ball-milling was confirmed by tracing the chemical state of Nb and was further supported by TEM observation. The reduced phases may act as more effective catalysts improving the desorption properties.