Arsenius Apostolius (Greek: Ἀρσένιος Ἀποστόλιος or Ἀρσένιος Ἀποστόλης; c. 1468 – 1538) was a Greek scholar who lived for a long time in Venice. He was also bishop of Monemvasia in the Peloponnese.
Arsenius Apostolius was the son of Michael Apostolius. He was born about 1468 in Crete and in 1492 he moved to Italy.
In 1506 the Roman Curia appointed Arsenius as Eastern Rite bishop of Monemvasia, at that time part of the regions subjected to the Venetian Republic. Arsenius declared himself in communion both with the Patriarch of Constantinople and with the Catholic Church. This position was untenable for the Church of Constantinople and Patriarch Pachomius I of Constantinople invited Arsenius to abdicate. The issue went on for more than two years until June 1509, when Pachomius excommunicated Arsenius, who retired to Venice.
In Venice Arsenius became a friend of Erasmus of Rotterdam and collaborated with Aldus Manutius. Arsenius later travelled widely in Italy and Greece until he died in Venice in 1538.