The semaphorin gene family plays important roles in axonal guidance in vertebrates and invertebrates. Semaphorin 2a, a member of the semaphorin family, belongs to class 2, which is found only in invertebrates. In our study, semaphorin 2a was cloned from the ant Polyrhachis vicina Roger. The full length of P. vicina semaphorin 2a (Pv-sema-2a) is 2763 base pairs (bp) and it contains a 5′-untranslated region (UTR) 92 bp long and a 3′-UTR 521 bp long. The open reading frame of Pv-sema-2a encodes a 716-amino-acid protein with a predicted molecular mass of 81.1 kilodaltons. Real-time quantitative reverse-transcription – polymerase chain reaction indicated that Pv-sema-2a mRNA is differentially expressed during P. vicina development, in the whole bodies as well as the heads of different castes. The high mRNA levels in embryos and pupae suggest that Pv-sema-2a plays an important role in ant development.