Identification key of bats (Chiroptera) from Switzerland based on hair structure observed through optical microscope. - The identification of mammalian hairs by microscope remains an efficient and well-known technique, but only a few studies concern bats. We studied hair morphology of the 29 species listed from Switzerland and present a dichotomic identification key based on overhair morphology observed by using optical microscopes. This key allows to identify most of the genera and also some typical species. The final purpose of this key is to give the possibility to analyse and to identify quickly the hairs found in guano, taken from their bat roosts.