The author of the dissertation described two unpublished so far hand written musical Oktoihs (Znamenny chant) of the Old Believers from his private collection. Based on those manuscripts the author indicates the important codicological and paleographical features of musical writing of the Theodosian and Pomorian Old Believers. Furthermore, the author presents the structure of the Oktoih book used by the Old Believers and makes overview of the polish literature concerning the discussed issues. The aim of the dissertation is to encourage other collectors of ancient manuscripts to share their collections and elaborations with researchers.