Alonso de Fonseca y Ulloa (also Alonso I de Fonseca) (died 1473) was a Roman Catholic prelate who served as Bishop of Ávila (1445–1454), Archbishop of Seville (1454–1465 and 1469–1473), and Archbishop of Santiago de Compostela (1465–1469).

In 1445, Alonso de Fonseca y Ulloa was appointed by the King of Spain and confirmed by Pope Eugene IV as Bishop of Ávila.^[1][2] On 4 February 1454, he was appointed by Pope Nicholas V as Archbishop of Seville.^[1] In 1465, he was appointed by Pope Paul II as Archbishop of Santiago de Compostela.^[1] In 1469, he was appointed by Pope Paul II to his prior position as Archbishop of Seville where he served until his death in 1473.^[1]

While bishop, he was the principal co-consecrator of Pedro González de Mendoza, Bishop of Calahorra y La Calzada (1454).^[1]

• Cheney, David M. "Archdiocese of Santiago de Compostela". Catholic-Hierarchy.org. Retrieved June 16, 2018. (for Chronology of Bishops) ^{[self-published]}
• Chow, Gabriel. "Archdiocese of Santiago de Compostela (Spain)". GCatholic.org. Retrieved June 16, 2018. (for Chronology of Bishops) ^{[self-published]}
• Cheney, David M. "Archdiocese of Sevilla {Seville}". Catholic-Hierarchy.org. (for Chronology of Bishops) ^{[self-published]}
• Chow, Gabriel. "Metropolitan Archdiocese of Sevilla (Italy)". GCatholic.org. (for Chronology of Bishops) ^{[self-published]}
• Cheney, David M. "Diocese of Ávila". Catholic-Hierarchy.org. Retrieved June 16, 2018. (for Chronology of Bishops) ^{[self-published]}
• Chow, Gabriel. "Diocese of Ávila". GCatholic.org. Retrieved June 16, 2018. (for Chronology of Bishops) ^{[self-published]}