Summary Introduction: Arnica flowers are used in pharmaceutical and cosmetic industry. According to EMA only endangered Arnica montana provides the medicinal plant material. However, some European countries also allow the use of A. chamissonis flowers, whose chemical composition is not known in detail. Objective: The aim of the study was to recognize and compare the chemical composition of A. montana and A. chamissonis flowers collected from plants cultivated in Poland. Methods: HPLC-DAD-ESI/MS analysis comprised phenolic acids, flavonoids and sesquiterpene lactones. Results: Thirty eight flavonoids and phenolic acids were recognized and quantified, with patuletin, 6-methoxykaempferol and quercetin present only in A. chamissonis flowers. Moreover, helenalin and acetyl-dihydrohelenalin were identified. Conclusion: A. montana and A. chamissonis flowers from plants grown in Poland possess similar composition of simple phenols and polyphenols, present in concentration slightly higher in A. montana. Helenalin and dihydrohelenalin esters identified in arnica flowers from various regions of Europe were not detected.