The article presents the content of the private letters of J. Piazza, Nuncio for Poland, residing in Troppau, to the Vicar Apostolic to the north (for the area of Northern Germany), Bishop A. Steffani, in the years 1706-1708. Letters show difficult circumstances in which Piazza had to fulfil his duties of the Nuncio after the abdication of King Augustus II. According to the viewpoint of papal diplomacy, he supported the right of Augustus as a legitimate ruler to the Polish throne. These private letters provide us with numerous detailed information included in the official reports that Piazza prepared for the Secretary of State.