Arsinoe III Philopator (Ancient Greek: Ἀρσινόη ἡ Φιλοπάτωρ, which means "Arsinoe the father-loving", 246 or 245 BC – 204 BC) was Queen of Egypt (220 – 204 BC). She was a daughter of Ptolemy III and Berenice II.

Between late October and early November 220 BC she was married to her brother, Ptolemy IV. She took active part in the government of the country, at least in the measure that it was tolerated by the all-powerful minister Sosibius. In 217 BC, she accompanied Ptolemy IV at the Battle of Raphia. When the battle went poorly, she appeared before the troops and exhorted them to fight to defend their families. She also promised two minas of gold to each of them if they won the battle, which they did. She was the mother of Ptolemy V. In summer, 204 BC she was murdered in a palace coup, shortly after the death of her husband. Eratosthenes wrote a manuscript called the Arsinoe, which is lost, the subject being a memoir of the queen. It is quoted by many ancient scholars.

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