Psamtik III (flourished 6th centurybce) was the lastking (reigned 526–525bce) of the 26thdynasty (664–525bce;seeancient Egypt: The Late period [664–332bce]) ofancient Egypt, who failed to block the Persian invasion of 525 and was later executed for treason.

The 5th-century-bce Greek historianHerodotus, the primary source for knowledge of the reign, states that in 525bce, after only six months on the throne, Psamtik confronted a Persian invasion led by KingCambyses II. After the enemy had crossedSinai with the aid of the Arabs, a bitter battle was fought atPelusium, a city onEgypt’s eastern frontier. The Egyptians with their mercenaries were compelled to withdraw toMemphis, the traditional capital, nearCairo. Cambyses besieged the city and captured it, seizing Psamtik. The former king was initially well treated, but he was later executed forconspiracy against the Persians.