Our aim in this study was to further the under-standing of the taxonomic relationships and the evo- lutionary history of grey voles (subgenus Microtus, or arvalis species group) by establishing a cytochrome b (cytb) phylogeny with special emphasis on three species occupying Southwest Asia: Microtus mystacinus (levis is a synonym), Microtus obscurus and Microtus transcaspicus. Phylo genetic trees yielded a sister position of Microtus arvalis + M. obscurus against M. mystacinus while, M. tran-scaspicus emerged as their closest relative. Microtus ilaeus hold a basal position in the subgenus. The only sample from Afghanistan was classified into M. transcaspicus, therefore expanding the known geographic range for the species and questioning the presence of Microtus ilaeus in the country. Deep sub-structuring was typical of all the well-sampled species: M. mystacinus, M. obscurus and M. arvalis. Kimura 2-parameter (K2P) genetic diver-gence of 4.1% between the two main clades of M. mys-tacinus [the European (EU) and our new Iranian (IR)] was nearly identical to a distance (4.2%) between M. arvalis and M.  obscurus, therefore suggesting undetected cryptic species in M. mystacinus. Our results reflect the importance of the Caspian-Altai zone for a speciation of the grey voles and of the Ponto-Caspian region for the intraspecific diversity of M. obscurus and M. mystacinus. M. arvalis is the only grey vole which diversified outside Asia.

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