Bi 0 . 4 3 Pb 0 . 3 5 Cu 0 . 2 2 O y glasses with different Cu + contents were prepared by melting at different temperatures. The glass structure consists of [BiO 3 ] and [BiO 6 ] units and the ratio of [BiO 3 ]/[BiO 6 ] increases with increasing Cu + content. The glass transition temperature, the first crystallization temperature peak, and the thermal stability of the glasses decreases with increasing Cu + content. The value of the activation energy, E a , varies as a function of the Cu + content. The crystallization mechanism in the glasses is closely related to the glass structure, which is mainly affected by the Cu + content.