Abstract: The effectiveness of a commercial modified geosynthetic clay liner (GCL) for the containment of the red mud leachates is investigated. The hydraulic conductivity (k) of GCL permeated with red mud leachate is an important index reflecting its containment performance. A series of free swell tests are conducted to evaluate the free swell index (FSI) of bentonite of the GCL in four types of red mud leachates. A series of modified fluid loss tests are conducted to evaluate k of the GCL using four types of red mud leachates as permeating liquids. The clean tap water is tested as a benchmark for comparison purpose. The influence of prehydration methods on k of the GCL sample are assessed. The results indicate that the FSI decreases with the increasing ionic strength (I). The k of non-prehydrated GCL is about 5 times that of the prehydrated GCL. The prehydration of GCL with tap water is suggested to achieve superior hydraulic performance exposed to the red mud leachate. The results show that k decreases slightly with the increasing air pressure and FSI, while it increases with the increasing I and relative abundance of monovalent and divalent cations (RMD). In the tested red much leachates, the hydraulic conductivity ratio (k in red mud leachate to that in tap water) of the GCL is found to vary within 4.35 to 12.0.