Eric II Valdemarsøn (c. 1290 – 12 March 1325) was Duke of Schleswig from 1312 until his death in 1325. He was the only son of Valdemar IV, Duke of Schleswig.
Eric was born c. 1290 as the only legitimate son of Duke Valdemar IV of Schleswig in his first marriage with Elisabeth of Saxe-Lauenburg, a daughter of John I, Duke of Saxony. Already during the lifetime of Valdemar IV, he acted as his father's coruler and used the title of duke.
At the death of Valdemar IV in the spring of 1312, he immediately succeeded his father as Duke of Schleswig. Shortly afterwards, he participated in the expedition of his feudal overlord, King Eric VI of Denmark, to Rostock. During this expedition, on 30 June in the camp outside Warnemünde, he was formally installed as Duke.
As Duke, he claimed the fief of Langeland after his deceased uncle, Eric Longbone, Lord of Langeland. These and other disputes with King Eric, were settled at the settlement in Horsens on 9 August 1313, in which Eric renounced his claims to Langeland but received the Crown lands of the Duchy of Schleswig.
When King Eric VI of Denmark died in 1319, Duke Eric was briefly candidate to the vacant throne of Denmark. Ultimately, Eric VI's brother, Christopher, was elected King. However, part of the price Christopher had to pay to accede to the throne, was to accept the right of Duke Eric to the fief of Langeland.
Duke Eric died on 12 March 1325. He was buried in the Schleswig Cathedral.
In 1313 Eric married Adelaide of Holstein-Rendsburg, a daughter of Henry I, Count of Holstein-Rendsburg.