Abstract The aim of this study was to investigate polyphenolic composition of different parts (leaves, flowers and fruits) of Crataegus almaatensis Pojark, an endemic plant of Kazakhstan, and compare it to a well known European Crataegus oxyacantha L. flowers. A Qual-Quant analysis was performed based on HR-MS measurements on 22 secondary metabolites: flavonoids and phenolic acids. Another goal was to evaluate the antioxidant potency of hawthorn extracts which was expressed in the total phenolic content and DPPH scavenging potency tests. Leaf extracts from C. almaatensis were found to be the most rich in metabolites and the most active in antiradical tests (IC₅₀ value of 48 μg/ml and TPC of 218 mg/g). The weakest potential was determined for the fruit extract of this species. According to the performed principal component analysis (PCA), the fruit extracts were not correlated with other organs of the plant, and the metabolites responsible for the extracts’ differentiation were cyanidin 3-glucoside and quetcetin 3-galactoside. Based on a high correlation factor, the flowers of the Kazakh species was found to be as rich in polyphenols as the European hawthorn. The results of this study indicate that C. almaatensis is a promising source of natural antioxidants.