ENThe personal archive of Michał Kleofas Ogiński (1765-1833), deposited at the Russian State Archives of Ancient Acts, was delivered to the Russian Imperial government by his son Ireneusz Ogiński after the death of his father in 1833. This archive preserved sources of his musical life, mostly documents from M. K. Oginski's life in Vilnius and Zalesye, supplemented and systematized during his life in Florence where composer spent the last years of his life. The musical collection of M. K. Ogiński is a collection of documents with unique historical value, which corrects and supplements previous knowledge about musical views and musical environment of politician and composer M. K. Ogiński. The historical value of the archive is derived not only from preserved manuscripts and first editions of M. K. Oginski's composing, but also wide contextual material, opening plentiful opportunities for new research and learning about M. K. Oginski's musical life. Documents preserved in this archival foundation allow to reconstruct the repertoire of the favourite works of M. K. Ogiński, and also supplement and specify knowledge perceived from the 'Letters about Music'. Musical sources of varying content reveal the scope of composer's views and intensity of his musical life, providing new information about his Florence period of life and creative work.