Effects of elevated CO₂ (twice ambient) on the interspecific competition among three species of wheat aphids (Sitobion avenae, Rhopalosiphum padi, and Schizaphis graminum) and on wheat-aphid interactions were studied. Wheat plants had higher biomass and yield and lower water and nitrogen content of grain when grown under elevated CO₂ than under ambient CO₂; levels of condensed tannins, total phenols, and total nonstructural carbohydrates were also higher in wheat ears under elevated CO₂. Compared with ambient CO₂, elevated CO₂ increased the abundance of R. padi when introduced solely but reduced its abundance when S. avenae was also present. The spatial distribution of wheat aphids was apparently influenced by CO₂ levels, with significantly more S. avenae on ears and a more even distribution of R. padi on wheat plants under elevated CO₂ versus ambient CO₂. Elevated CO₂ did not affect the abundance and spatial distribution of S. graminus when inoculated solely. Moreover, when S. avenae was present with either R. padi or S. graminum, spatial niche overlap was significantly decreased with elevated CO₂. When three species co-occurred, elevated CO₂ reduced spatial niche overlap between S. avenae and S. graminum and between R. padi and S. graminum. Our results suggest that increases in atmospheric CO₂ would alleviate interspecific competition for these cases, which would accentuate the abundance of and the damage caused by these wheat aphids.