The glass-forming region of the BiO1.5-PbO-CuO system has been determined by the melt-quenching technique. The glass transition temperatures, T-g, and the first crystallization peak temperatures, T-x1, are around 240 degrees C and 285 degrees C, respectively. The glass structure consists of [BiO3] and [BiO6] units, and the conversion between these polyhedra mainly depends on the CuO and PbO content. The covalent characteristic in the infrared absorption spectra of the [PbOn] pyramidal units becomes significant when the glass contains more PbO.