Investigations were carried out in the years 2012–2014 on arable fields in western Ukraine in order to evaluate the occurrence of Ambrosia artemisiifolia L. in the stands of: (1) corn (Zea mays L.); (2) sunflower (Helianthus annuus L.); (3) alfalfa (Medicago sativa L. subsp. sativa); (4) strawberry (Fragaria x ananassa Duchesne); (5) potato (Solanum tuberosum L.); (6) spring wheat (Triticum aestivum L.); (7) soybean (Glycine max (L.) Merr.) and (8) grapevine (Vitis vinifera L.). Phytosociological and syntaxonomic assessment of the segetal communities was carried out with the Braun-Blanquet method at the height of the vegetative season. The study demonstrated Ambrosia artemisiifolia to predominate amongst the weeds occurring in the analyzed crops, and that area coverage with this plant reached 85–90% in the fields of spring wheat, sunflower and corn. Weeds occurring on the investigated arable fields were identified to belong to 7 syntaxonomic classes.