The permeability of bentonite and bentonite-sand is an essential parameter for designing any type of waste disposal or in geo-environmental engineering applications. To design and construct these facilities accurate values of permeability for these bentonite-sand mixtures must be evaluated. For this purpose, a series of various laboratory tests was performed to investigate the coefficient of permeability using direct and indirect test methods derived from consolidation theory using variable liquid limit (1.10 ~ 2.00) of bentonite. Permeability tests were also carried out for dynamically compacted bentonite and bentonite-sand mixtures. In this paper a discrepancy between permeability determined by direct and indirect test methods was identified. In some cases the coefficient of permeability varied to a maximum of about 10 times between the direct and indirect test methods at the same void ratio and also varied within the same method. The void ratio of the bentonite was a key parameter of permeability for bentonite and bentonite-sand mixtures. The specimen manufacture method had no effect on permeability. This study proposes a formula to predict the coefficient of permeability for bentonite slurry by knowing the degree of saturation for a given void ratio.