This article deals with the verification of ecotoxicity of nanomaterials on the basis of selected clay minerals (montmorillonite, kaolinite) and quartz as a reference substance. The ecotoxicity was determined by the inhibition of marine bacteria Vibrio fischeri, with relationship to the particle size and concentration of minerals in water leachate prepared according to Council Decision 2003/33/EC. Statistically significant dependence between inhibition of Vibrio fischeri and the concentration of minerals in water leachate was found for montmorillonite.