Due to easy vegetative and generative reproduction, the most part of the Cirsium species are considered as common weeds in different kinds of crops, on meadows and pastures. They owe their success in acquiring new area, both morphological and physiological characteristics, such as the production of allelopathic substances. An example the species within of the Cirsium genus, which may have the allelopathic properties, is cabbage thistle C. oleraceum (L.) Scop. It is a common meadow perennial plant, which in disturbed habitats quickly becomes expansive species, eliminating the other components of the flora. Such phenomenon is well-documented on the meadows of the Ojców National Park (Southern Poland). Therefore, it was investigated the effect of aqueous extracts of dried leaves C. oleraceum on seed germination, seedlings growth, the fresh and dry weight and the water content of the seedlings in three meadow species: Trifolium pratense L., Lolium multiflorum Lam. and Dactylis glomerata L. The results showed that C. oleraceum exhibits the allelopathic potential, which may have limited effect on the studied parameters of fodder species, but only when using high concentrations of extracts prepared from the leaves (15% and 20%). D. glomerata was the most sensitive on the C. oleraceum allelopathic substances.