One of the most important characteristics of a backfill material is the particle size distribution. In this paper, the authors have focused the effect of deslimed mill tailings on paste backfill performance at a copper-zinc mine in northeast Turkey. The use of sedimentation methods to deslime has a widespread utilisation and regarded as a true fractional size analysis practice. The common laboratory method of beaker decantation was used for desliming in order to determine the optimum particle size distribution. For studying the beaker decantation, two mine tailings, namely tailings samples A and B are used which have particles 52 and 54 wt.% finer than 20 mum, respectively. The fines content (-20 mum) of each tailing were reduced to 15, 20, 25 and 30 wt.% via desliming. Deslimed tailings then were tested to investigate the relationship between particle size and strength gain. It was found that strength ranges of the deslimed tailings were from 12% to 52% higher than as-received mill tailings. (C) 2003 Elsevier Ltd. All rights reserved.