Zr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass with a diameter of 2mm was prepared by copper-mould casting. The microstructures of the bulk alloy were examined by X-ray diffraction, optical microscopy and high-resolution electron microscopy. It was found that the structure of the bulk metallic glass formed by copper-mould casting is actually Dot homogeneous, but composed of three different regions: a purely amorphous portion which makes up the major part of the bulk sample; a second portion containing a few of very small particles in the amorphous matrix, and a third portion consisting of the quasicrystals in the amorphous matrix. The formation of quasicrystal during casting of the melt involved the inward diffusion of Zr and outward diffusion of Ni and Cu. The icosahedral short-range order is likely to have already existed in the glassy state of Zr65Ni10Cu7.5Al7.5Ag10 alloy after casting. (C) 2004 Elsevier B.V. All rights reserved.