Alphonso IV (died 933), by-named the Monk, was King of Leon from 924 to 931.
He was the eldest son of Ordono and possibly born posthumously. He did not ascend upon his father's death as his was too young. However his uncle Fruela's death in next year made him the king as he was the eldest among the children of Ordono and Fruela. Having a faint personality, he resigned the crown to his brother Ramiro and went into a religious house. A certain instability of character is revealed by the fact that he took up arms with Fruela's son against Ramiro, having repented of his renunciation of the world. He was defeated, blinded and sent back to die in the cloister of Sahagun. Ordono IV of Leon was his son.