Leopold III. (* 1073; † 15. November 1136) was the margrave of Ostarrichi in the years 1065 to 1136. He is the [Landespatron] of Austria.
He was the son of Ida von Formbach-Ratelnberg and margrave Leopold II., because he supported him against his father Heinrich IV.
His most important foundation is Klosterneuburg, which has been built in 1108.
Other important foundations, which helped him for his canonisation in the year 1485, were Heiligenkreuz Abbey, Klein- Mariazell and Seitenstetten Abbey.
He was buried in the Klosterneuburg Abbey. 1663 he became [Landespatron] Austrias instead of Hole Kolomann.