The casting Ni-25 Al-xFe alloys had dendritic microstructures, and the two major phases existing in these alloys were 132 (ordered b.c.c.) phase in dendrites and f.c.c. phase in interdendrites. The 132 phase exhibited a higher hardness and was more brittle by comparison with the f.c.c. phase in interdendrites, and the two phases showed different plastic deformation results during tensile test. Cracks nucleated at the interfaces between these two phases during tensile stress, then propagated and the specimen failed. The room temperature tensile fracture modes were a mixture of dimple and cleavage. Changing the testing temperature or the mole fraction of elements in the alloys changed the fracture mode and mechanical properties. (C) 2002 Elsevier Science B.V. All rights reserved.