Abstract <p>The search for natural antioxidants owing to their role in minimizing the harmful effects of oxidative stress on the human body is becoming more and more relevant. The hypothesis of the increased level of secondary metabolites in invasive species has been put forward, because in the secondary range the plants grow under stressful environmental conditions. Targeted screening of the most aggressive invasive species for the presence of substances of antioxidant activity in them was carried out. The DPPH method was used to determine the antioxidant activity of extracts of leaves (51 samples) and inflorescences (56 samples) of 39&#xa0;invasive plant species collected in different regions of Europe. It has been shown that all investigated invasive species actively inhibit oxidative processes and, therefore, can form antioxidant defense under oxidative stress. Alcoholic extracts of inflorescences of all <i>Solidago</i> species and <i>Ailanthus altissima</i> and alcoholic extracts of leaves of <i>Solidago</i> species, <i>Veronica filiformis</i>, and <i>Sorbaria sorbifolia</i> have the highest antioxidant activity. In aqueous solutions, the antioxidant activity is in general somewhat lower: the greatest amount of substances with antioxidant activity was observed in the leaves of <i>Reynoutria</i> × <i>bohemica</i>, <i>Ribes aureum</i>, and <i>Sorbaria sorbifolia</i> and in the inflorescences of <i>Reynoutria</i> × <i>bohemica</i> and <i>Ailanthus altissima</i>. Owing to their high antioxidant activity, the invasive plants are a promising resource for use in medical practice.</p>