Diego de Rojas (died 1544) was a 16th-century Spanish Conquistador.
He was born in Burgos and traveled to the city of Santo Domingo in 1516. In 1522 went to Mexico under the command of Hernán Cortés, and subsequently formed part of the conquistador army of Pedro de Alvarado, participating in the conquests of what is now Mexico, Guatemala and El Salvador.
In 1536 Rojas traveled to what is now Peru, as part of a corps of relief to help the army of Francisco Pizarro in the Spanish conquest of the Inca Empire. Between 1538 and 1539 he participated in the conquest of the province of Charcas, in present-day Bolivia. After Ciudad de la Plata de la Nueva Toledo was founded he became its first governor. He became Justicia Mayor and along with Lope de Aguirre explored the territory of the Ch'unchu people.
In 1543 he explored the Rio de la Plata with 200 men at the orders of the governor of Peru Cristobal Vaca de Castro. He died shortly afterwards in 1544 from the effects of a poisoned arrow in Santiago del Estero.