The barrier liner system is the most important element in designing a landfill. In developed countries, a number of natural and artificial materials are used for barrier liner materials in consideration of specific conditions of each landfill. However, clay and HDPE are mostly used in Korea. This study evaluates the physical and dynamic properties of water-quenched slag generated in large quantities in many domestic industrial sites, an alternative material for clay liner in the final cover system. Then, the study assesses whether the material has appropriate permeability coefficient (k), uniaxial compressive strength and environmental impact to meet the relevant regulations. By changing the mixing ratio of additives (bentonite, cement) to the main ingredient of water-quenched slag, the study suggests case 6 as an optimal mixing ratio. Accordingly, various indoor experiments are conducted for the mixtures to analyze the adequacy of the design standard for the final cover system liner. The results shows that the outcome fell within the standard set by the Waste Disposal Act in Korea. The uniaxial compressive strength was measured for different curing periods (7, 14 and 28 days); the second sample showed the highest strength of 22.5 kgf/cm2, and other mixtures resulted in overall improvement in strength as all samples met the design standard of 0.5 kgf/cm2 for the landfill cover system. The study identified an optimal mixing ratio (slag : 39%, clay : 50%, bentonite : 8%, cement : 3%) that meets the legal provision of the Waste Disposal Act in Korea. The material in this study has a potential to be recycled extensively, and even creates additional value. Therefore, this study verified that the water-quenched slag can be used as environment-friendly liner for the final cover system in landfill.