Ulrich III of Regenstein-Heimburg

Ulrich III of Regenstein-Heimburg (c. 1287–1322/23) was a count of the Regenstein line in the Harz, holding the county of Heimburg and the lordship of Derenburg. He was the son of Count Albert I of Regenstein and Sophie of Lippe.

In 1308 he married Sophie of Anhalt-Aschersleben. Their marriage produced sixteen children, including his successors Bernhard I and Albert II of Regenstein, and he died around 1322–1323.