Microstructure and ageing characteristics of a cast Zn-Al based alloy (ZnAl7Cu3) were studied using X-ray diffraction, electron scanning microscopy and back-scattered diffraction techniques. Two stages of phase transformation, i.e., decomposition of zinc rich eta phase and four phase transformation, alpha + epsilon --> T' + eta, were detected during ageing at 150degreesC. Electron back-scattered diffraction technique was applied in distinguishing both zinc rich eta and epsilon phases. (C) 2003 Kluwer Academic Publishers.