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Cosmos sulphureus is an adventitious species for Europe and Ukraine in particular. It originates from Central and South America, where it grows in tropical and subtropical climates. The climatic conditions of Kyiv are characterized as temperate, with an absolute temperature minimum of –32.2 °C, an absolute maximum of +39.9 °C, and average annual rainfall of 649 mm. Plants were analyzed in the flowering phase, divided into inflorescences, leaves, stems, and roots, dried at +35 °C and then extracted with methanol and water. The determination of the antiradical activity was carried out according to a modified method using a DPPH (2,2-diphenyl-1-picrylhydrazyl) radical inhibition reaction. The highest antiradical activity was detected in inflorescences (59.60–81.81 % inhibition) and leaves (79.81–89.12 % inhibition). Stem extracts had an average level of inhibition (19.63–65.93 %), and root extracts showed only 2.54–39.46 % inhibition. Correlation analysis showed a strong relationship between leaves and stems (r = 0.84), leaves and roots (r = 0.81), and stems and roots (r = 0.91). Extracts of C. sulphureus plants grown in temperate climate were found having a high antioxidant potential but lower than that reported for tropical and subtropical regions. It was found that higher intensity of coloration of marginal florets of the capitulum does not correlate with a higher antiradical activity. Methanolic and water extracts of inflorescences of the genotype CSCO-368812 with intensilly colored perianth inhibited only 59.60 % and 71.50 % of radicals, while similar extracts of the genotype CS-361294 with lighter florets inhibited 71.17 % and 81.81 % of radicals, respectively. Instead, there was a difference in antiradical activity depending on applied extractant. Methanolic extracts of vegetative organs (leaves, stems, roots) prevail over water extracts in terms of their antiradical activity. However, water extracts of inflorescences of both genotypes demonstrated higher level of antiradical activity.