A first synopsis of lichenicolous fungi of Mongolia based on new collections and literature data is provided, including 114 species. Five new species are described: Capronia cogtii (on Vahliella leucophaea), Echinothecium hypogymniae (on Hypogymnia bitteri), Feltgeniomyces mongolicus (on H. bitteri), Phacopsis vulpicidae (on Vulpicida juniperina) and Roselliniella javkhlanae (on Rinodina turfacea var. ecrustacea). Two new combinations are proposed: Endococcus hafellneri (≡ Stigmidium hafellneri) and Sphaerellothecium taimyricum (≡ Sphaerellothecium thamnoliae var. taimyricum). Unidentified specimens of Acremonium (on Mycoblastus sanguinarioides), Cercidospora (on Rhizoplaca chrysoleuca s.lat.), Didymocyrtis (on Rhizoplaca chrysoleuca s.lat.), Lichenochora (on Physcia alnophila), Lichenostigma (on species of Xanthoparmelia), Phoma (on Vulpicida juniperina) and a leotialean fungus (on Cetraria laevigata) are characterized and discussed. Taxonomic notes are provided for Cercidospora macrospora s.lat., Didymocyrtis cf. melanelixiae, Minutoexcipula cf. beaglei, Nesolechia cetrariicola, Sphaerellothecium cf. parmeliae and Stigmidium cf. psorae. Sphaeropezia intermedia is newly reported for Eurasia. Didymocyrtis grumantiana is newly reported for Asia. Additionally, 71 species of lichenicolous fungi and five species of lichenicolous lichens are documented in Mongolia for the first time. Allocetraria is reported as a new host genus for Abrothallus peyritschii, Vulpicida for Arthonia triebeliae, and Anamylopsora for Muellerella pygmaea.