Alexander
Duke of Schleswig-Holstein-Sonderburg
Born	20 January 1573 Sønderborg
Died	13 May 1627(1627-05-13) (aged 54) Sønderborg- Beck
Spouse	Dorothea of Schwarzburg-Sondershausen
Issue	John Christian, Duke of Schleswig-Holstein-Sonderburg Ernest Günther, Duke of Schleswig-Holstein-Sonderburg-Augustenburg August Philipp, Duke of Schleswig-Holstein-Sonderburg-Beck Philip Louis, Duke of Schleswig-Holstein-Sonderburg-Wiesenburg
House	Schleswig-Holstein-Sonderburg
Father	John II, Duke of Schleswig-Holstein-Sonderburg
Mother	Elisabeth of Brunswick-Grubenhagen

Alexander, Duke of Schleswig-Holstein-Sonderburg, (20 January 1573 – 13 May 1627) was a Danish nobleman.^[1]

Alexander was born in Sønderborg (German: Sonderburg) in Schleswig, the third son of John II, Duke of Schleswig-Holstein-Sonderburg and Elisabeth of Brunswick-Grubenhagen. Because his elder surviving brother chose Ærø as his seat, Alexander received Sønderborg upon their father's death and was in practice its second duke. Alexander died in Sønderborg.

Alexander married Dorothea of Schwarzburg-Sondershausen,^{[citation needed]} daughter of John Günther I, Count of Schwarzburg-Sondershausen, on 26 November 1604 in Oldenburg. They had eleven children:^{[citation needed]}

• John Christian (26 April 1607 – 28 June 1653)
• Alexander Henry (12 September 1608 – 5 September 1657)
• Ernest Günther (14 October 1609 – 18 January 1689)
• George Frederick (18 December 1611 – 23 August 1676)
• August Philipp (11 November 1612 – 6 May 1675)
• Adolph (2 November 1613 – 1 February 1616), died young
• Anna Elisabeth (5 February 1615 – 19 February 1616), died young
• William Anton (2 April 1616 – 2 April 1616), died soon after birth
• Sophie Katharina (28 June 1617 – 22 November 1696), wife of Anthony Günther, Count of Oldenburg
• Eleonore Sabine (27 February 1619 – 27 February 1619), died soon after birth
• Philip Louis (27 October 1620 – 10 March 1689)