Estrogen receptor-related receptors (ERRs) belong to a subfamily of orphan nuclear receptors where the proteins are closely related to the estrogen receptors (ERs) in structure. ERR homologs have been found in many animals and play an important role in the regulation physiologic processes. We have isolated the ERR homolog, abbreviated as PvERR, from the ant Polyrhachis vicina Roger (Hymenoptera: Formicidae). The full-length cDNA of the PvERR gene is 1,918 bp, containing a 5′-untranslated region (5′-UTR) of 245 bp and a 3′-UTR of 368 bp. The open reading frame of 1,305 bp encodes a 434-amino acid protein. The PvERR gene is composed of eight exons and seven introns. The tertiary structure of both the DNA binding domain and the ligand binding domain (LBD) of PvERR belong to the α β type. The LBD of PvERR is formed by 11 α-helices without H2, and it is similar to the mammalian ERRγ LBD of known crystal structure. Further investigation indicated the potential significance of PvERR in the regulation of development in P. vicina, due to its expression in different developmental periods and castes.