Fertilization has impact on the growth of crops and weeds. The aim of this paper was to broaden the knowledge about the influence of fertilization on the biology of the chosen weeds species. In the season of 2006–2007, floristic composition, numbers and biomass have been estimated in winter rye monoculture, in different fertilization systems. Rye monoculture had been investigated since 1923 on an experimental field SGGW in Skierniewice. Various doses of mineral and organic fertilizers were applied. The highest weed infestation level was observed on the plots with mineral fertilizers along with manure, which were used once in a 5 year’s period. In all treatments, the following dominant weed species were recognized: Centaurea cyanus, Lithospermum arvense, Viola arvensis, Matricaria inodora, Anthemis arvensis, Galium aparine. In particular treatments, no significant differences in floristic composition were identified. Taking into consideration various treatments, significant differences in the height and biomass of weeds were found. Differences in the number of the observed weed species amongst different treatments were found as well.