The aim of the study was to analyse the content of phenolic acids, total phenolic compounds, proanthocyanidins, and antioxidant capacity in cotyledons and hypocotyl of five cultivars of common buckwheat (Fagopyrum esculentum Moench) sprout. This study presents the first broad profile of phenolic acids occurring in buckwheat microgreen seedlings. In the hypocotyl and cotyledons trans-cinnamic acid and its derivatives: o-, m-, and p-coumaric acids (2-, 3-, and 4-hydroxycinnamic), synapic acid (4-hydroxy-3,5-dimethoxycinnamic), caffeic acid (3,4-dihydroxycinnamic), and two isomers of ferulic acid (4-hydroxy-3-methoxycinnamic and 3-hydroxy-4-methoxycinnamic) have been identified. Among the benzoic acid derivatives hydroxybenzoic, protocatechuic (3,4-dihydroxybenzoic), gallic (3,4,5-dihydroxybenzoic) and syringic (4-hydroxy-3,5-dimethoxybenzoic) were found in the organs. In addition to those mentioned, the organs of buckwheat sprouts contain chlorogenic acid as well. The contents of all analysed phenolics were substantially higher in the cotyledons than in the hypocotyl of buckwheat sprouts, except for chlorogenic and caffeic acids. Trans-cinnamic acid was the major phenolic acid in both organs. In the cotyledons, a significant, positive linear correlation between the TEAC, ORAC, PLC-ACW values and content of total phenolic compounds, and also between DPPH and total phenolic acids were found. In the hypocotyl correlations between the DPPH, TEAC, and ORAC and proanthocyanidins content, between TEAC and total phenolic compounds, and between total phenolic acids and PCL-ACW were found.