The key design parameters of cemented paste backfill (CPB, a mix of tailings, water and binder) are strongly influenced by its saturated hydraulic conductivity (permeability). However, our understanding of the permeability of CPBs, as well as factors that affect it and its evolution with time, is limited. Hence, a laboratory investigation is conducted to study the hydraulic conductivity of CPBs and develop a model for predicting its evolution with time. The results show that the hydraulic conductivity of CPB is time-dependent. As the curing time increases, the hydraulic conductivity decreases. The permeability is also affected by the mix components. The permeability decreases as the binder content increases or the w/c ratio decreases. Medium tailings with 45% fine particles confer lower hydraulic conductivity to the CPB. The sulphate can have two opposite effects on the permeability of CPBs, contributing to an increase or decrease. However, the magnitude of the influence of the mix components depends on the curing time and is generally more pronounced at early ages (<= 7 days). Moreover, this study demonstrates that the hydraulic conductivity decreases with curing temperature and time for the studied CPBs. However, the effect of curing temperature on the hydraulic conductivity of CPBs is more significant in early age samples (up to 7 days) and depends on the binder type. Furthermore, the mechanical damage can significantly increase the hydraulic conductivity. Finally, the authors propose a simple function for the prediction of the evolution of the hydraulic conductivity of CPB with time. The validation results show that the developed model is able to predict the time-dependent change of the hydraulic conductivity with good accuracy. (C) 2009 Elsevier Ltd. All rights reserved.