Subject and purpose of work: Monitoring of biological diversity within the areas of natural value is targeted at assessment of the impact of the applied agricultural practices on the natural environment. The aim of the research was to compare species diversity and abundance of segmental plants occurring in winter cereals grown in the selected ecological farms and conventional farms in the Lubelskie voivodeship. Materials and methods: Monitoring research were conducted between 2012-2014 in 28 farms (14 ecological and 14 traditional) on fields with cereal crops. Species composition and volume of habitats of weeds was defined as well as diversity indicators of Shannon-Wienner and Simpson were indicated. Results and conclusions: Research indicated that diversity of segmental flora which accompanies cereal was larger in ecological farms than in the traditional ones. The total of 149 species of weeks were marked; 107 taxa were common for both farming systems, 26 were characteristic for ecological system while 16 for the traditional farming. It was noted that the significantly larger number of species present in the field and the volume of weed per area unit was present in ecological farming. Both within the traditional farming system and the ecological one more monocotyledons than dicotyledonous species were found. The assessment of flora diversity via Shannon-Weinner and Simpson indicators indicated larger species diversity in fields of arable crops in ecological system than the conventional one, however, no significant dominance of one or more species of weeds was noted in case of either of the systems.