GPCRs play crucial roles in the growth, development and reproduction of organisms. In insects, a large number of GPCRs have been reported for Holometabola but not Hemimetabola. The recently sequenced pea aphid genome provides us with the opportunity to analyze the evolution and potential functions of GPCRs in Hemimetabola. 82 GPCRs were identified from the representative model hemimetabolous insect Acyrthosiphon pisum, 37 of which have ESTs evidence, and 73 are annotated for the first time. A striking difference between A. pisum, Drosophila melanogaster and Tribolium castaneum is the duplication of the kinin and SIFamide receptors in A. pisum. Another divergence is the loss of the sulfakinin receptor in A. pisum. These duplications/losses are likely involved in the osmoregulation, reproduction and energy metabolism of A. pisum. Moreover, this work will promote functional analyses of GPCRs in A. pisum and may advance new drug target discovery for biological control of the aphid.