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Geosynthetic clay liners (GCLs) are widely used in landfill and other engineering projects as waterproof materials due to their low hydraulic conductivity when in contact with water.However, GCLs are now often expected to contain mining liquids with low pH, and an assessment of GCL performance to acidic liquids is required. The hydraulic conductivity of a commercial Australian geosynthetic clay liner has been evaluated under various effective pressures and concentrations of sulfuric acid solutions. In our study, we modified the traditional flexible wall testing equipment by installing pH and EC sensors in the influent and effluent lines to determine automatically the in/out-flow pH/EC values and therefore assess chemical equilibrium in real time. All the values are compared with the values obtained with water as permeant. The results show that the hydraulic conductivity values increased significantly with the increasing concentrations of acid solutions, the elevated effective stress improved the hydraulic performance of GCLs. All the chemical compatibility tests were conducted on non-prehydrated GCLs.