Ferns dwelling in the South Siberia territory appear to be ancient, the time of their origin is most likely dated the Upper Cretaceous – Palaeogene. Apparently, since that time the formation of the pteridoflora of South Siberia has been started. During the Tertiary period there was a gradual formation of the fern flora through migrations intensified in the Neogene in the time of mountain ranges building. The migrations were: from the eastamerican-european and westamerican-eastasian sectors of Holarctic; partly from Central Asia. Evidently, 6 species of 59 formed right in the territory of South Siberia. They might have formed after disconnection of widely ancestors' areas with the following isolation of separated parts, through adaptation to changed climate, and isolation of races in ecologically differed habitats. The Quaternary glaciation impacted greatly the process of South-Siberian flora formation developing into species extinction and their areas shrinking. In the Postglacial period there was a secondary colonization of fern species from refugia or other sites within which they had survived the glaciation throughout the territories that became ice-free.