This paper presents the results of investigations on changes of the parameters of coal and surrounding rocks in the fault zones in the Upper Silesia Coal Basin. It has been shown that these zones, in relation to the undisturbed coal seams, reveal a n enrichment with some substances that pose a threat to the natural environment and that they also show a deterioration in the strength parameter values of rocks which threaten the safety of the operation. The greatest threat for the environment constituted sulphur and the ash. In the zone of the fault, it wa s observed that sulphur behaved in two ways. In the first case, the total sulphur and pyritic sulphur increased significantly by 192.3 and 823.5 %, respectively, and a small quantity of sulphate sulphur was found here, whereas in the other case, the total sulphur and pyritic sulphur decreased by 31.6 an d 35.3 %, respectively, and sulp hate sulphur increased considerably and reached up to 600 %. The mean content of ash increased by 171.8 %. The mechanical strenght of the rocks under uniaxial compressive strength in the fault zones decreased by 67 %, the microhardness of coal decreased to zero, and the intensity of cracks in coal grains increased by 359.1 %., Stanisław Roman Cmiel., and Obsahuje bibliografické odkazy