The author analyzes two non-canonical prayers and Glagolitic Abecedarium in that the newly found Glagolitic manuscript Psalterium Demetrii Sinaitic. The Glagolitic Abecedarium is a very important for Glagolitic writing, especially when compared to other Abecedaria. Orthographical and morphological features of the two prayers are analyzed in this paper to test the hypothesis that the manuscript had older Serbian or Croatian archetypes. The analysis of the linguistic features suggests an Old Bulgarian origin.