The paper introduces an unknown work by Clement of Ohrid devoted to St Alexis of Rome included in the Slavic Festal Menaion ) 25, 14th c., from the collection of Monastery At Catherine, Mount Sinai (Sin. Slav. 25). The Sinai copy of the Office of St Alexis contains three stichera in mode 1 and a troparion in mode 8 in the Vesper part of the office, and a kanon in mode 8 for the Orthros. The kanon contains the name of Clement into acrostic КЛИМ.