The aim of the study was to evaluate the weed infestation of maize grown in mixed sowing with other plant species (sunflower, common bean, vetch). The field experiment was carried out in the years 2014-2016 at the ecological farm in Chwałowice, belonging to the Advisory Agricultural Center in Radom, using the randomized block method, in 4 replications, on the soil of the good wheat complex, class IIIa. An assessment of species composition, species abundance, fresh and air dry weed weight and biomass index were determined. The analysis showed that the mix sowing of maize with different plant species significantly reduced weed infestation. The highest weight of weed was found in maize cultivation in pure sowing. The most competitive with weeds was maize grown in mix sowing with sunflower, where weed weight was reduced by 36% compared to pure maize sowing. The number of weed species in the maize cultivated in mixed sowing of the studied crop species varied considerably over the years of the study. Most weed species were identified in the first year of the study (average of 23 species), characterized by high moisture content, and the lowest in the third year of the study (average of 8 species). The lowest values of the biomass index for the three years of the study were found for control and maize grown with common bean. While the largest for maize grown in mixed sowing with sunflower.