Nanostructured MnFe2O4 was prepared by high-energy ball milling of a stoichiometric mixture of MnO and Fe2O3 powders and characterized by XRD, TEM and TGA techniques. The ball milling process leads to strained nanocrystals with an average size of about 5 nm, agglomerated in sizes of about 100 nm. It was used with mechanically activated Na2CO3 to produce hydrogen from water in the temperature range 973-1073 K. At 1023 K the mixture shows a hydrogen production five times higher than that obtained with manganese ferrite prepared by thermally activated solid-state reaction. (c) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.