Increasing atmospheric CO₂ concentration is expected to enhance the grain yield of C₃ cereal plants, while at the same time reducing the concentrations of minerals and proteins. This will lead to a lower nutritional quality and increase global problems associated with micronutrient malnutrition. Among the barley grain storage proteins, the C-hordein fraction has the lowest abundance of sulfur (S) containing amino acids and is poorest in binding of zinc (Zn). In the present study, C-hordein-suppressed barley lines with reduced C-hordein content, obtained by use of antisense or RNAi technology, were investigated under ambient and elevated atmospheric CO₂ concentration. Grains of the C-hordein-suppressed lines showed 50% increase in the concentrations of Zn and iron (Fe) in the core endosperm relative to the wild-type under both ambient and elevated atmospheric CO₂. Element distribution images obtained using laser ablation-inductively coupled plasma-mass spectrometry confirmed the enrichment of Fe and Zn in the core endosperm of the lines with modified storage protein composition. We conclude that modification of grain storage proteins may improve the nutritional value of cereal grain with respect to Zn and Fe under both normal and future conditions of elevated atmospheric CO₂.