This paper aims to analyze the antioxidant activity and phenolic content of cereal concentrates from corn and oat and to investigate issues related to import regulation. The phenolic composition was examined by liquid chromatography-high-resolution mass spectrometry, and the antioxidant activity was determined using the spectrophotometric method and expressed as µmol of Trolox equivalent antioxidant capacity per kg of extract. The cornmeal flour was found to contain almost twice as much phenolic compounds as the oatmeal flour, despite comparable antioxidant activity (range, 800-900 µmol Trolox kg-1 extract). The phenolic content of grain was 550-650 mg CE 100 g-1 extract; it was statistically lower compared to flour samples and statistically higher compared to cracker samples. The presence of 9 flavonoids and 4 phenolic acids was found in all tested samples of flour and crackers. The phenolic acids content of grain ranged from 380 to 3010 mg kg-1; most of them (up to 80-90%) were bound. The incidence of mycotoxins in positive samples (excluding grain) was as follows: 8%, patulin; 4%, nivalenol/deoxynivalenol; 34%, aflatoxins; 6%, zearalenone; 31%, ochratoxin A; 17%, fumonisins. The concentration ranged from 0.5 to 10 µg/kg. The present findings can be useful to optimize food formulations and improve product stability during transportation.