Nitrogen absorption and desorption properties as well as possible formation of a non-equilibrium phase were investigated on Ca-Fe powder prepared by ball milling (BM) method. The milled Ca-Fe powder absorbed and desorbed more amount of nitrogen than pure Ca powder and pure Fe powder when each was separately milled and processed. The amount of nitrogen absorbed and desorbed by the Ca-Fe powder is increased with milling time and its magnetization significantly decreased. The large reduction in the magnetization is explained by formation of the non-equilibrium alloy phase in the Ca-Fe powder system, where the new phase is capable of absorbing and desorbing nitrogen and has its magnetization significantly less than pure Fe. © 2004 Elsevier B.V. All rights reserved.