Lichens are understood to be symbiotic organisms consisting of mycobiont and photobiont partners. This mutual partnership results in the production of unique secondary metabolites, which are used in contemporary pharmacy and medicine. The purpose of this study is to explore the uses of lichens in a particular period of medieval pharmacology: it retraced the relevant Arabic terms for, and descriptions of, lichens in the Kitab al-Saydanah fi al-Tibb , the “Book of Pharmacy in Medicine” written by Abu Rayhan Muhammad ibn Ahmad al-Biruni (973-1048). It will be shown that al-Biruni used اشنة ( ushnah ) for naming epiphytic lichens and حزاز الصخر ( hazaz al-sakhr ) for saxicolous ones. The information about lichens transmitted in his text is in accordance with that of his contemporary Ibn Sina, the famous physician and philosopher. In that period, the study, transmission and updating of the legacy of Antiquity promoted and influenced the use of lichens in Arabic and Islamic pharmacology and medicine. Keywords: Islamic medicine – lichens –medieval pharmacy – medieval botany – al-Biruni – materia medica.