This paper presents the effect of physical, chemical and mineralogical properties of tailings and binder using two different sulphide tailings (Tailings T1 and T2) and Portland cement based pozzolanic binders (B1 and B2) on the unconfined compressive strength (UCS) of cemented paste backfill (CPB) samples in the short and long terms. A total of 144 paste samples were prepared using different binder proportions of 4-7% by dry weight to determine an optimum CPB mixture with a target UCS of >= 0.7 MPa at a curing time of 28 days. The results have shown that the short-term strength development of paste backfill samples is dependent inherently on the properties of tailings and binder used. A general trend of increase in the short term strength of CPB samples was noted to occur with the decrease in the water-to-cement ratio. The paste backfill samples prepared only from Tailings T1 with 7 wt.% B1 type binder content were found to have a maximum UCS of 0.75 MPa while the samples obtained from Tailings T2 and Binder B2 produced consistently low UCSs of <0.7 MPa, which could be attributed to the high water retention potential of Tailings T2 and the additive content of Binder B2. However, the long term performance of Binder B2 appeared to be better than that of Binder B1 with 40-42% loss of its 180-day strength at a 360-day curing period compared with only 9-14% loss for Binder B2 apparently due to the lower pozzolanic material content of the latter. These findings have revealed that physical, chemical and mineralogic properties of tailings and binders are of fundamental importance for the strength development and stability of paste backfill material in the short and long term. (C) 2005 Elsevier B.V. All rights reserved.