Christian August I, Duke of Schleswig-Holstein-Sonderburg-Augustenburg (4 August 1696 – 20 January 1754) was the duke of Schleswig-Holstein-Sonderburg-Augustenburg, member of a cadet branch of the House of Oldenburg.

Christian August was a son of Frederick William of Schleswig-Holstein-Sonderburg-Augustenburg, who was himself a son of Ernest Günther, and his wife, Countess Sophie Amalie of Ahlefeld-Rixingen (1675-1741), herself a daughter of Count Frederick of Ahlefeldt-Rixingen.

He served as provost of the cathedral chapter in Hamburg.

Later, he became governor of the Danish island Als, then General of the Infantry and Colonel of the royal guards in Denmark.

He married Countess Frederikke Louise of Danneskiold-Samsøe (1699–1744), the daughter of Count Christian Gyldenløve by his first wife and cousin, Countess Charlotte Amalie of Danneskiold-Laurvig (1682-1699).