Six soil profiles have been selected from the area of Zitny Ostrov for the identification of mineralogy of the clay fraction. The main mineral association obtained was illite, and chlorite with small admixtures of kaolinite. The day fraction also contains some dastogenic minerals like quartz and feldspars. Carbonates (calcite and dolomite) of clastogenic and authigenic origins represent very important constituents of the clay fraction. This mineralogy has a great influence on the soil properties of the area studied.