The aim of the experiment was to analyze the effect of several intercrop plant species on the yielding of spring barley in many-year monoculture. A field experiment was conducted in 2001–2003 in Czesławice (Lublin Agricultural University). The experiment was localized on loess soil classified as the second evaluation class. The soil was characterized by light acid reaction and a very high content of available forms of phosphorus, potassium and magnesium. Two forms of barley naked and husked were tested. The other factors were treatments with intercrops for ploughing: A – without intercrop (control treatment), B – white mustard, C – spring vetch and field pea, D – rye grass. Protection of the canopy consisted of seed dressing and mechanical removal. In the protection herbicides, fungicides, insecticides and growth regulators were additionally applied. The sowing rate for both forms of barley was identical and equalled 300 grains per one square metre. It was proved that the highest crop of intercrop dry weight was obtained through the seeding of spring vetch, field pea as well white mustard. Rye grass proved to be the least suitable for intercrop cultivation. The cultivation of intercrops in spring barley monoculture stimulated the production of the cereal seed. The highest yields were obtained from husked barley. The ploughing of white mustard followed by the ploughing of leguminous plants mixture had the most beneficial effect on spring barley yield structure. The cultivation of white mustard intercrop proved to be the most effective way of reducing weed infestation of spring barley.