The article is devoted to the study of a manuscript book of the middle of the 17th century, kept in the collection of E.E. Egorov in the Manuscripts Department of the Russian State Library and containing the text of the Slavonic translation of Josephus Flavius’ “The Jewish War”. This copy, which remained unaccounted for in the domestic historiography of the monument, is accompanied by additional articles, one of which, dating back to the “Tale of the Princes of Vladimir”, which remained unknown until now, is introduced into the scientific turnover. The owner of the book, judging by the entry in its margins, was Prince Dmitry Vasilyevich Romodanovsky, exiled in 1660 to the Solovetsky Monastery.On the basis of a review of manuscripts belonging to the family of D.V. Romodanovsky and a comparison with one written by him himself, it is proved that the prince also produced the manuscript of Egorov. It is assumed that it was written by D.V. Romodanovsky still at home, before his exile to the Solovetsky monastery. It was possible to read in ultraviolet rays the erased record on the protective sheet, which testifies to the fact that the manuscript was put up for sale in the 17th century. An attempt is made to find the antigraph of additional articles of the book, particularly in the libraries of the Solovetsky Monastery and the Romodanovskys. It is concluded that it is necessary to introduce the manuscript under study into a wide scientific circulation as an important historical source.