ENThe object described in the article is the bilingual Lithuanian-Polish Catholic postil written by Konstantin Sirvid (c. 1579–1631) – Lithuanian Jesuit, preacher, author of a dictionary of the Lithuanian language and the first original sermons in the Lithuanian language in aboriginal Lithuania. Writing original sermons, he contributed to the development of the Lithuanian literary language. He is also considered to be the creator of the standard orthography in Lithuania. The aim of the study is to analyze graphy and orthography used in the Polish text. Description, however, of only one part of the Polish postyl would be incomplete. Therefore, in the first part of the study we will focus on the analysis of Polish graphy and orthography (with specific reference to phonetics), and the second part will attempt to trace some similarities in the recording systems of Polish and Lithuanian text, detecting Polish interference on the Lithuanian orthography. This will be the subject of discussion in the next publication.