Plants introduce chemicals into the environment that can be toxic, both for themselves and for other species. Weed infestation of crops is a competition for environmental resources, but at the same time is a source of chemical substances released into the soil, often reducing yield potential. The paper attempts to investigate the allelopathic interaction of aquatic extracts from dry shoots of chickweed Stellaria media L. on germination and development of maize Zea mays L. seedlings of ‘San’, ‘Kidemos’ and ‘DKC 3441’ cultivars. Along with the increase in the concentration of allelopathic substances, a decrease in the germination activity of all tested maize cultivars was observed. Germination percentage as like percentage of control was the highest for seeds germinating on substrates with 1% chickweed extracts and the lowest for seeds watered with 5% extracts. Biometric measurements of seedlings showed that the most sensitive cultivar of maize was ‘DKC 3441’, and the resistant cultivar ‘San’. The relative water content was the highest for seedlings grown on the 5% extracts. Significant differences in the amount of fresh and dry masses of maize seedlings were demonstrated at the highest concentrations of extracts compared to the control. A significant increase in electrolyte leakage compared to the control sample was found in the ‘Kidemos’ cultivar. The lowest differences in the destabilization of the ionic transport through cell membranes for the ‘DKC 3441’ cultivar were demonstrated. ********* In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 3, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue. *********