Barley and oat grains in addition to beta-glucan contain antioxidant phytochemicals such as phenolic compounds that have health beneficial properties. The aim of this study was to investigate the impact of growing location on the composition of phenolic compounds and its antioxidant activity in barley and oats. Barley varieties included Compass, Gairdner and Hindmarsh grown in Condobolin, Northstar and Oaklands. Oat varieties included Echidna, Williams and Yallara grown in Condobolin, Wagga Wagga, and Oaklands. Findings: Cultivation environment was observed to have a significant impact on the total phenolic content and antioxidant activity of both cereals. In barley, proanthocyanidin content was also affected by cultivation location. Variable response of phenolic compounds to cultivation location indicated a genetic influence. In barley, several phenolic compounds were affected by location and genotype, including flavonoids and proanthocyanidins, such as prodelphinidins. In oats in addition to flavonoids, avenanthramide A, B, and C were also affected by environmental conditions. Conclusion: Phenolic compounds found in barley and oats that were susceptible to environmental conditions are the major contributors of antioxidant activity. The study also outlines the possibility that both genetic and environmental factors affect the regulation of phenolic compounds in cereals. Significance and novelty: This study contributes to the understanding of phenolic compound response to growth conditions while highlighting the importance of monitoring the impact environment can have on compounds of interest.