In order to determine the effect of quench-ageing treatment on the microstructure and properties of Zn-15Al-3Cu alloy, it was prepared by permanent mould casting and then solution treated at a temperature of 330 degrees C, quenched and aged at 180 degrees C. The changes in the microstructure, length, hardness, strength and ductility of the quenched alloy were monitored during ageing. The microstructure of the alloy in the as-cast condition consisted of beta dendrites and alpha, eta and epsilon phases. However, solution treatment followed by quenching removed the lamellar microstructure of the alloy and produced a supersaturated beta solid solution. Subsequent ageing resulted in transformation of beta solid solution to alpha and eta phases and conversion of metastable epsilon phase to stable T' compound. Appropriate ageing times for T6 and T7 heat treatments of this alloy have been determined according to the experimental results.