Ptolemy Keraunos (Ceraunus) (? - 279 BC), King of Macedon from 281 BC to 279 BC.

He was the eldest son of Ptolemy I Soter (ruler of Egypt) and his third wife Eurydice (daughter of Antipater). His younger brother Ptolemy II became heir apparent and, in 282 BC, the new pharaoh. Ptolemy Keraunos had left Egypt and arrived at the court of Lysimachus, the king of Thrace, Macedonia, and part of Asia Minor. His half-sister Arsinoe II of Egypt was wife of Lysimachus.

After Lysimachus' defeat and death in the battle of Corupedium in 281 BC, against Seleucus I Nicator, Ptolemy Keraunos murdered Seleucus I. In 281 BC he made an alliance with Pyrrhus of Epirus. Ptolemy asked his half-sister Arsinoe II, the widow of Lysimachus, to marry him. After the ceremony he killed Arsinoe's two younger sons and Arsinoe II herself fled to Egypt and married her own brother Ptolemy II.

Ptolemy Keraunos was killed in war against the Gauls of Brennus.

Keraunos is Greek for "Thunder".