EN„Prosta mova” was an official East Slavic language of the Grand Duchy of Lithuania. Texts in „prosta mova” were written in different graphics systems: Cyrillic, Latin and even Arabic letters. The article is devoted to the earliest texts in „prosta mova” written by Latin alphabet. Reasons for such texts, their characteristics and spesific features are analysed. The author considers such texts hybrid ones, and proves that they were not only transliterated, but original ones, too. Keywords: The Grand Duchy of Lithuania, Belarusian Latin alphabet, the East Slavic languages, «prosta mova», graphic system, hybrid texts.