Otto III, Count of Weimar-Orlamünde

Otto III, sometimes numbered Otto IV (1244–1285), was an Ascanian count of Weimar-Orlamünde, the son of Herman II. In 1248 he and his elder brother Herman III inherited the estates of their maternal uncle, Otto II of Merania; the partition left Otto with Weimar and Plassenburg and Herman with Orlamünde.

In 1279 he founded Himmelkron Abbey. He married Agnes of Truhendingen, died in June 1285 and was buried in the abbey's church.