The article refers to the spelling of texts from the collection of the Duchy of Opole and Racibórz, gathered in the State Archives in Wrocław. This collection is among highly important testimonies of using Czech language in Upper Silesian chancelleries, and includes lesser known documents and books from the period between the end of 15th century and the year 1731. Many of them are texts from the 16th century. In the initial phase of its systematic elaboration the features of the transcription of postalveolar sibilants and affricates (including ř) from the 16th texts were analyzed. They determine the type of orthography in the handwriting model and the level of its efficiency. The spelling of consonants š, č, ž, ř in these texts does not differ from Czech and Moravian sources (Porák, 1983), but it is closer to the spelling in manuscripts from the first half of the 16th century — conservative and often ambiguous (which may make difficult to interpret regional features of the language). Some stylistic and functional differences in these texts are worth noticing — the more precise the text, the more functional its diacritic spelling.