Francesco Sanseverino, the proud mayor of Grassano, where de Blasio's grandmother was born, was quoted in Gazzetta del Mezzogiorno as saying that the honour was being bestowed on the New Yorker due to the "feeling of pride and belonging" he has to his roots.
De Blasio, who replaced Michael Bloomberg as mayor of New York, will receive the honorary citizenship during a ceromony in Grassano on July 24th.
He will visit the town as part of a nine-day holiday in Italy, which will also include a visit to his grandfather's home town of Sant'Agata de' Goti, near Naples.
His grandparents, Anna Briganti and Giovanni de Blasio, emigrated to the United States in the early 1900s.
The ceremony in Grassano will begin at around 2pm and will be attended by the town's mayor as well as Marcello Pittella, the president of Basilicata. A local singer called Vittoria Sigillino will sing the US national anthem.