The paper presents results of water permeability tests of burnt coal mining wastes and their mixtures with fly ash. The test materials were: coal mining wastes from the landfill of the coal mine KWK Gliwice, fly ash from the Skawina Power Plant SA and mixtures of the coal mining wastes with the ash in which the ash content was 10, 20 and 30% (by weight). The basic geotechnical characteristics of the tested materials were determined basing on the results of the tests carried out according to standard procedures. The tests of water permeability of coal mining wastes and their mixtures with fly ash were carried out in a medium size apparatus. Analysis of the results of tests was carried out in the aspect of usability of the tested waste materials for earth structures.