The Persian Gospel codices of the Matenadaran collection, written in Armenian script in the eighteenth century in Shamakhi and Ganja, are important sources for the study of the interethnic, interfaith, and intercultural circumstances of historical Shirvan (located in Transcaucasia) of that period. These manuscripts are also considered to be essential sources for the study of inter-linguistic issues of Armenian and Persian, the Armenian orthographic rules of that period, and one of the local versions of Persian, spoken in Shirvan. In the eighteenth century, Persian was the interethnic contact language of this area and the manuscripts examined here were written for the Christian Armenians of the region. This article presents how the Armenian alphabet reflects the phonetic system of eighteenth century Persian spoken in Shirvan using the orthographic rules of Armenian.