Grains of three cultivars of each cereal: winter wheat (Triticum aestivum L. – Tonacja, Bogatka, Satyna), winter rye (Secale cereae L. – Stanko, Dańkowskie Złote, Amilo) and winter barley (Hordeum sativum L. – Laverola, Mertada, Merk) were examined. In addition, phenolic acids were identified in these grains, and the content of the identified acids, i.e. ferulic, vanillic, p-coumaric, protocatechuic, p-hydroxybenzoic, syringic, sinapic and caffeic, was determined. The antioxidant properties of phenolic acids were examined using the free radical scavenging method against a stable 2.2-diphenyl-1-pikrylhydrazyl radical (DPPH). The antiradical efficiency of phenolic acids depended on the duration of a reaction and genotype-specific properties. The data showed that different winter cereal seed extracts were able to quench 15-47% of DPPH radical solution and to exhibit potent radical scavenging activity. Results of the determinations of the content of phenolic acids in grains of the cultivars correlated with the activity of their extracts. The tested cereal grains were characterized by different levels of the identified phenolic acids, depending on the generic and specific characteristics. Differences in the content of phenolic acids may be subject to genetic traits, environmental factors and different analytical procedures. Cereal kernels with a higher phenolic acid content also exhibited a higher antioxidant activity of extracts with these compounds. Kernels of winter barley cv. Metaxa with a higher content of phenolic acids were also characterized by higher antioxidant activity than those of cvs. Merle and Laverola. The lowest content of phenolic acids was observed in winter rye cv. Stanko. 5-day seedlings showed a statistically significant increase in phenolic acids (ferulic, p-coumaric, protocatechuic, p-syringic, sinapic and caffeic) and the high antioxidant activity. Winter cereal seed extracts were able to quench 15-47% of DPPH radical solution and exhibited potent radical scavenging activity.