The distribution of weeds in maize hybrids grown in different crop densities with and without herbicide application was observed in the present study. The floristic composition and structure of weed community were estimated according to the occurrence of distributed weed species, number of their plants and their mass per area unit. These parameters were monitored as they more precisely determine competitive effects of different maize crop densities on weeds. Furthermore, effects of mentioned factors on maize grain yield were studied. The analysis of variance for the RCB design, within statistical and biometrical procedures, alongside with LSD- and t-test, as a correlation analysis between dry weight of weeds and maize plant height and grain yield were used for data processing in relation to the observed densities and hybrids (Steel and Torrie, 1960). Obtained results indicate that the increase of crop densities statistically significantly affected decreasing of the number of plants per species and weight of weeds. In comparison with the nontreated variant, the variant with herbicide application showed that this application resulted in significant decrease of weed species, number of plants per species, fresh and dry weight. The number of weed plants per species was higher in the hybrid H₁ (ZPSC 42A) than in the hybrid H₂ (ZPSC 704) in both years. The average maize plant heights statistically significantly differed in dependence on the herbicide application and a hybrid. The crop density affected leaf area, leaf area index and number of leaves per maize plant. Grain yield of maize was the highest in the highest density (D₃) when herbicides were applied (T) and in the hybrid H₂ during both years of investigation.