Competition ability of wheat cultivars towards weeds is important for weed management, especially under an integrated and ecological production system. An attempt to assess winter wheat (Kobra cultivar) competition ability towards weeds is presented in the paper. The results were collected from a field experiment conducted on nutrient-rich and brown loess soil by split-plot method in the 1995/96–1997/98 seasons. Winter wheat Kobra cultivar was sown in a half field area (designed for crops) and the other half was left as fallow. Both cropped and uncropped parts of the field were treated in the same way by experimental factors and agrotechnical measures. Experimental treatments concerned weed management, they were: A – no treated; B – harrow after wheat emergence (autumn); C – harrow in tillering stage (spring); D – herbicide (thifensulfuron-metyl 40.92+chlorsulfuron 4.09 g ha-1) in tllering stage, and combination of the treatments: BC; BD; CD; BCD. Biomass produced by plants on the cropped field (grain, straw, chaff, weeds) and uncropped one (weeds) was collected from 1 m2 (2 m × 0.5 m) of each plot at winter wheat harvest time (the end of July), then it was dried in a glasshouse and weighed. There is higher biomass production per 1 m2 on the cropped (mean 1450.3 g) than on the uncropped (fallow) field (in average 702.3 g) under nutrient-rich and brown loess soil. Winter wheat Kobra cultivar components (grain, straw, and chaff) constituted 93.7% of the total air dry weight produced under control plots (not weeded out), which allows to accept the cultivar as highly competitive to weeds. The contribution of wheat dry mass increased to 98.9% of the total mass when the weed control became more and more intensive; however, the gain in wheat weight is not so high in comparison to inputs to the weed control, especially by herbicide. Simplified competition index used to assess the ability of wheat to compete with weeds needs more extensive research and calibration.