Nabû-nāṣir, inscribed in cuneiform as dAG-PAB or dAG-ŠEŠ-ir, Greek: Ναβονάσσαρος, whence "Nabonassar", and meaning "Nabû (is) protector", is the king of Babylon 747–734 BCE.

He deposes a foreign Chaldean usurper named Nabu-shuma-ishkun, bringing native rule back to Babylon after twenty-three years of Chaldean rule.

His reign sees the beginning a new era characterized by the systematic maintenance of chronologically precise historical records.

Both the Babylonian Chronicle and the Ptolemaic Canon begin with his accession to the throne.

He is contemporary with the Assyrian kings Aššur-nirarī V (755–745 BCE) and Tiglath-Pileser III, the latter under whom he becomes a vassal, and the Elamite kings Humban-Tahrah I (–743 BC) and Humban-Nikaš I (742–717 BC)