Alessandro Mattei (20 February 1744, Rome – 20 April 1820) was an Italian Cardinal, and a significant figure in papal diplomacy of the Napoleonic period. He was from the Roman aristocratic House of Mattei. He became Archbishop of Ferrara in 1777, and was named cardinal in 1779. He became Bishop of Palestrina in 1800, Bishop of Porto-Santa Rufina in 1809, and Bishop of Ostia in 1814. From 1817 to his death he was archpriest of St Peter's Basilica.