Bentonite is one of the essential materials involved in the disposal of highly toxic chemical and radioactive waste in deep underground facilities. Bentonite is often a key component of the engineered barrier system for high level waste or spent fuel disposal and has a wide range of application, increasingly in the area of environmental management. The coefficient of permeability of bentonite and of a mixture of bentonite and sand is an essential parameter in the design of any type of waste disposal facilities. A series of standard and high pressure consolidation tests have been performed using different liquid limits for bentonite and bentonite-sand mixtures in order to observe the coefficient of permeability derived from consolidation theory. The coefficient of permeability has also been measured by the falling head method. It was found that the permeability varied at the same void ratio due to the use of a different method of computation. The liquid limit of the bentonite and the content of sand in the bentonite-sand mixture played is a key component in the coefficient of permeability.