Diego Merino, O. Carm. (1570 – 1 January 1637) was a Roman Catholic prelate who served as Bishop of Isernia (1626–1637) and Bishop of Montepeloso (1623–1626).
Diego Merino was born in Baeza, Spain in 1570 and ordained a priest in the Order of the Brothers of the Blessed Virgin Mary of Mount Carmel. On 20 November 1623, he was appointed during the papacy of Pope Paul V as Bishop of Montepeloso. On 26 November 1623, he was consecrated bishop by Giovanni Garzia Mellini, Cardinal-Priest of Santi Quattro Coronati with Alessandro Bosco, Bishop of Gerace, and Tommaso Ximenes, Bishop of Fiesole, serving as co-consecrators. On 24 August 1626, he was appointed during the papacy of List of popes as Bishop of Isernia. He served as Bishop of Isernia until his death on 1 January 1637.
While bishop, he was the principal co-consecrator of Giulio Cesare Sacchetti, Bishop of Gravina di Puglia (1623) .