Alfonso I or Alphonso I may refer to:
Alfonso I of Asturias (739–757), king of Asturias Alfonso I of Aragon (1104–1134), known as Alfonso the Battler, king of Aragon and Navarre Alfonso I, Duke of Gandia (1332–1412) Alfonso V of Aragon (1396–1458), king of Naples as Alfonso I Alfonso I Piccolomini (1468–1498), duke of Amalfi Alfonso I d'Este, Duke of Ferrara (1476–1534)
See also Afonso I of Portugal (1094–1185), king of Portugal Afonso I of Kongo (1456–1543), first Christian king of the Kingdom of Kongo Alfonso XIII of Spain (1886–1941), known to French Legitimists as "Alphonse I"