Arnica montana L. is an endangered species rich in sesquiterpene lactones, phenolic acids and flavonoids with high pharmaceutical value. The polyphenolic content and free radical scavenging activity of plants that had passed all stages of cultivation: micropropagation and rooting (in vitro), adaptation in greenhouse (ex vitro) and mountain conditions (in vivo) were evaluated. Four surface flavonoid aglycones [scutellarein 6-methyl ether (hispidulin), scutellarein 6,4’-dimethyl ether (pectolinarigenin), 6-OH luteolin 6-methyl ether and kempferol-6-methyl ether] were detected in the acetone exudates of the studied samples bymeans of thin layer chromatography.No differences in the accumulation of surface flavonoids were found among the tested leaf extracts of in vitro, ex vitro and in vivo samples. However, the extracts from the flowers were richer in surface flavonoids than extracts from the leaves. The methanol extracts of the samples from ex vitro and in vivo grown A. montana plants had significantly higher radical scavenging activity and polyphenolic content than the extracts of in vitro samples. The observed differences in the contents of these biologically active compounds were related to different growth conditions and stages of plant development. The biotechnological method of A. montana established holds promise for the future production of antioxidants.