The author has analyzed the creative heritage of Sergei Bortkiewicz, indicating the publishing houses that collaborated with the artist (D. Rahter, Kistner & Siegel, N. Simrock, Ries & Erler, Rozsavölgyi, etc.), and tracing the fate of archives of the composer’s main publisher – Anton J. Benjamin. He concludes that the piano works were the most successful of his compositions that were published, whereas the songs, for example, rarely saw publication. Earlier works from Opus 3-33 were all published, whilst his later opuses from Op 34-74 saw only intermittent publication, the bulk remaining in manuscript. By processing documents containing a list of the artist’s works (including works previously unknown in Ukraine), it was discovered how many compositions remained unpublished, and where the manuscripts of these works were likely to be held. The storage location of these manuscripts – found to date and confirmed – include the archives of the Austrian National Library, the National Library of Spain, Gaetano Donizetti Music Library in Bergamo (Italy), the Netherlands Music Institute in the Hague, the E. Fleisher Collection in the Free Library of Philadelphia (USA), and the Saxon State Archive in Leipzig (Germany). In addition, the scholar was able to research the way in which these works were obtained by these establishments (sending by author, getting from another repository, etc.), and how they were eventually re-discovered (froma purposeful search in archival catalogs to a mere coincidence). Through German and Austrian newspapers, as well as the letters of the composer himself, the author was able to conduct research on references to planned performances, or future plans for publication of the lost works by Sergei Bortkiewicz, which in turn, helped to guide the assumption about their potential location.