Abstract: (George Martinuzzi Utyeszenics’s Death in the Report written by Francesco degli Streppati from Milan) The present paper deals with the narration of the the murder of George Martinuzzi Utyeszenics (Brother George) reported in the manuscript, Morte di Frate Giorgio, con alcune altre cose in Transsilvania et Ungaria successe negli anni 1551-1552, which is conserved at the National Library of Vienna. György Martinuzzi was born in 1482 in the castle of Kamičac, in Croatia. After a monastic experience, he went into the service of John Szapolyai, the king of Hungary, who at that time fought against the other king of Hungary, Ferdinand Habsburg. György Martinuzzi began his carrier at the court of King John: he was appointed great treasurer of the reign, and took the place of Imre Czibak in the management of the important bishopric of Várad/Oradea as well. After King John’s death and the transfer of the royal court to Transylvania (1541), Martinuzzi was also appointed lieutenant (voivode), supreme judge, guardian of the son of King John, commander-in-chief of the Transylvanian army; hence, he concentrated all the power in his hands. He was atrociously murdered on December 17, 1551 by the killers that Giovanni Battista Castaldo had engaged conforming to an order of King Ferdinand. The author of the manuscript, identified with the cavalryman Francesco degli Streppati from Milan, who, in the years 1551-1553, took part in the Transylvanian campaign against the Ottomans as General Castaldo’s secretary, refers to the events occured from the battle of Mohács (1526) till those ones which took place after George Martinuzzi’s death. The work of Francesco degli Streppati can be considered a primary source for the subsequent historical works, which were drawn up on the history of Transylvania of the sixteenth century