Two multi-component Laves phase hydrogen storage alloys containing a body centered cubic (BCC) solid solution phase, were prepared and the effects of annealing treatment on their crystal structures have been studied in this part. It is found by X-ray powder diffraction and energy dispersive X-ray spectrometer analysis that the as-cast alloys mainly consist of two phases: the C14 Laves phase matrix with hexagonal structure and the dendritic V-based solid solution phase with BCC structure. In addition, a small amount of TiNi-based third phase is also found precipitated within both the C 14 Laves phase and the V-based solid solution phase. However, the content of the TiNi-based phase is decreased greatly by an appropriate annealing treatment owing to the compositional homogenization. Furthermore, the lattice parameters and unit cell volumes of both the C14 Laves phase and the V-based solid solution phase have all increased after the, annealing treatment. (C) 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.