Total polyphenols content (TPC), antioxidant activity (AA) and polyphenolic spectrum assay of three underutilized fruit species—black crowberry (Empetrum nigrum), honeyberry (Lonicera kamtschatica) and European cranberry (Vaccinium oxycoccos) is the aim of the present work. TPC and AA assay was performed by spectrophotometry and "individual phenolic compounds" were established by high-performance liquid chromatography. The results showed that TPC ranged from 1.61 ± 0.16 (European cranberry) up

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... o 5.65 ± 0.01 (Black cowberry) gallic acid mg/g fresh weight. The highest value of DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging assay was determined in black crowberry fruit (7.43 ± 0.34 mmol TROLOX/g fresh weight of fruit). In all samples, the most prevalent phenolic acid was ferulic acid with the highest content in the samples of black crowberry (77.73 ± 3.99 µg/g FW of fruit), black crowberry and honeyberry were present by the highest level of gallic acid (21.82 ± 1.53; 15.07 ± 2.45 µg/g FW of fruit). Honeyberry represented a valuable source of quercetin (12.18 ± 7.88 µg/g FW of fruit), whereas European cranberry and honeyberry are a source of rutin (28.48 ± 0.83 and 27.99 ± 1.78 µg/g FW of fruit, respectively). The results of statistical analyses proved significant differences between cowberry and European cranberry in TPC content and in AA among assayed species. In the same way, statistically significant differences were confirmed in phenolic acids among the assayed species except for European cranberry-honeyberry (in trans p-coumaric, protocatequic and cinnamic acid) and honeyberry-cowberry (in cinnamic acid content). The catechin content is significantly influenced by species (p ≤ 0.05), on the other hand the species has no influence on the resveratrol content (p > 0.05). Each of the studied species can be considered as valuable source of total polyphenols and individual phenolic compounds. Polyphenolic compounds were most frequently accumulated in the vacuole as well as in the outer layers of pericarp.