Abstract—The article presents the results of a study of the effect of urban environment in the Donbass on the content of biologically active substances, heavy metals and antioxidant activity of the flowers of Crataegus fallacina Klok., a poorly studied non-pharmacopoeial species of the genus Crataegus L. Under technogenic pollution, in the flowers of C. fallacina a decrease in the concentration of carotenoids and an increase in the content of phenolic compounds (flavonoids, procyanidins, oxycinnamic acids, tannins, anthocyanins), ascorbic and free organic acids was detected. The hermetic response of the content of anthocyanins and procyanidins to the pollution level was observed. The flowers of C. fallacina have a high total antioxidant activity, which increases under technogenic load, indicating plants sufficient adaptation to the urbanized environment. The ability of C. fallacina plants to limit flow of cadmium and lead to generative organs was revealed. The concentration of mercury in flowers exceeds its concentration in soil. C. fallacina flowers harvested in the Donbass meet the regulations on the content of active substances and comply with the requirements with regard to the heavy metals content. The obtained results prove the practicability of using C. fallacina for pharmaceutical purposes along with pharmacopoeial species of the genus Crataegus, and the possibility of their harvesting for medicinal use in the Donbass.