Descurainia sophia is a winter or spring annual weed. Flixweed used to be described as a ruderal weed, where it occurred mainly in associantion Sisymbrietum sophiae Kreh 1925 and community Artemisietalia Lohm. apud R. Tx. 1947. However, recently this species has become one of the main weed species in the cultivated crops. The aim of the present research was phytosociological characterization s of segetal communities with flixweed. The research was connected with looking for Descurainia sophia in the agricultural crops cultivated in the Lublin region. Phytosociological records were made with the Braun-Blanquet’s method were made in the places of occurrence flixweed. All observations were carried out in the years 1997–2002. The weed species were characterized on the basis of the constancy (S) and cover coefficients (D). The classification of communities was based on Kornas system [1950]. The communities with Descurainia sophia were described as fragmentary communities, without characteristic species of associations. Flixweed occurred in communities belonging to combinations: Panico –Setarion, Eu -Polygono -Chenopodion, Aperion spicae -venti and communitie from order Secali -Violetalia arvensis. These communities grew mostly in winter cereals and winter rape, on 1, 2, 3 and 4 soil complex. Descurainia sophia was characterized by the highest cover coefficient in communities with Veronica persica from Eu-Polygono -Chenopodion combination (D=253), Papaver rhoeas – Consolida from Aperion spicae -venti combination (D=228), however, the smallest in communitie with Echinochloa crus -galli from Panico-Setarion alliance (D=73).