Four grain aphids, Sitobion spp. [S. avenae (F.), S. akebiae (Shinji), S. miscanthi (Takahashi) and S. fragariae (Walker)] on various grasses (Poaceae), nominated as Sitobion avenae-complex in this paper, were compared for their morphological and genetic characteristics. For morphological comparison, ten characters frequently used in the identification of S. avenae-complex were compared among samples from various global locations. The results from these comparisons demonstrated that the ranges of specific characteristics overlap considerably. The means of most characteristics were very similar among S. avenae, S. miscanthi and S. akebiae, indicating that the characteristics are not useful for the individual identification of these three grain aphids. Also, the intra-specific variations of the Far Eastern S. akebiae were as large as the inter-specific differences between S. miscanthi and S. avenae. In the nucleotide sequence comparison of the mitochondrial cytochrome oxidase subunit II (mt COII) gene, the pair-wise genetic distances among the populations of the three species ranged from 0.00 to 1.56%, almost equal to the intra-specific distances of Far Eastern S. akebiae (0.00–1.38%). In this context, it is suggested that S. akebiae (Shinji) syn. n. and S. miscanthi (Takahashi) syn. n. be synonymized under the senior name, S. avenae (F.).