Ernest August, Duke of Schleswig-Holstein-Sonderburg-Augustenburg (30 October 1660 – 12 March 1731) was the second son of Duke Ernest Günther and his wife Auguste.

Ernest August converted to Catholicism and became a canon in Strasbourg.

In 1692, he succeeded his childless brother Frederick as Duke of Augustenburg.

In 1695 he married Baroness Maria Theresia of Weinberg (d. 1712).

This article about a German duke is a stub.