Clays are essential materials to reduce the hydraulic conductivity of natural clay liners in landfill sites. Impermeable compacted clay liners are needed the landfill to be designed. It is known that clays with high plasticity absorb water several times as much as their weights. The clay liners subjected to water pressure in landfills generate high permeability in time and instability problems in their body due to their expansive capacity. Though the compacted clay liners possess many advantages such as low permeability and large capacity of attenuation, they have high shrinkage and high expansive potential causing instability problem. The aim of this study is to examine the effects of silica fume on permeability, swelling pressure and compressive strength of the compacted clay liners as a hydraulic barrier. The test results showed that the compacted clay samples with silica fume exhibit quite low permeability, swelling pressure and significantly high compressive strength as compared to raw clay samples. Thus, silica fume appears to be promising for construction material of liners subjected to leachate in solid waste containment systems. (C) 2004 Elsevier B.V. All rights reserved.