Onofrio Avellino (c. 1674 – 17 April 1741) was an Italian painter of the Baroque period.
Born in Naples, Giulio died in Ferrara or Rome, where he painted for the last twenty years of his life. He initially trained under Luca Giordano, but in 1692, when the former left to work in Madrid, he entered the studio of the Neapolitan Francesco Solimena. He painted a Virgin and Child, with Angels and Saints in Glory for the church of the Carmelitani in Sorrento. For a church of Vico, he painted a canvas of St Ciro and Giovanni and the Virgin. He painted two canvases, one of a Miracle of St Dominic and the Apparition of the Virgin to the Shepherdess, for the church of Rosariello delle Pigne, outside of the Porta di Gennaro. He also made copies of Giordano and Solimena for export.