Berberis vulgaris L. is currently widely studied for its antioxidant and chemopreventive proper-ties, especially given the beneficial properties of its fruits in this regard. Although the bark and roots have been well known and used in traditional medicine since ancient times, little is known about the other parts of this plant. The aim of the research was to determine the antioxidant and LOX inhibitory activity effects of extracts obtained from leaves, fruits, and stems. Another aim of the work was to carry out the quantitative and qualitative analysis of phenolic acids, flavonoid aglycones, and flavonoid glycosides. Extracts were obtained with the use of ASE (accelerated solvent extraction). The total content of polyphenols was determined and was found to vary de-pending on the organ, with the highest amount of polyphenols found in the leaves extract. The free radical scavenging activity of the extracts was determined spectrophotometrically in relation to the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical, with results ranging from 63.88 mgTE/g for leaves to 65.25 mgTE/g for the stem. Antioxidant activity was also assessed using the ABTS test. The lowest value was recorded for the barberry fruit (117.93 mg TE/g) and the highest level was found for the barberry leaves (140.49 mgTE/g). The oxygen radical absorption capacity test (ORAC) showed the lowest value for the stem (167.70 mgTE/g) and the highest level for the leaves (267.81 mgTE/g). The range of percentage inhibition of LOX was determined as well. The percentage inhibition of the enzyme was positively correlated with the sum of flavonoids, TPC, TFC, and the content of selected flavonoids. For the first time, phenolic acids, flavonoid agly-cones, and flavonoid glycosides were determined qualitatively and quantitatively in individual parts of Berberis vulgaris L. The content of phenolic acids, flavonoid aglycones, and flavonoid glycosides was determined with the LC-MS/MS method. For the first time, the following phenol-ic acids were quantitatively and qualitatively identified in individual parts of Berberis vulgaris: 3-caffeoylquinic acid, protocatechuic acid, 5-caffeoylquinic acid, flavonoid glycosides: eleuthero-side E, rutin, isoquercitin, luteoloside, nar-cissoside, naringenin-7-glucoside, isorhamnetin-3-glucoside, afzeline, and quercitrin. Flavonoid aglycones: catechin, luteolin, and eriodictyol were determined qualitatively and quantitatively for the first time as well.