Weimar-Orlamünde, sometimes called Otto IV (1244 – June 1285) was a German nobleman.

He was a member of the House of Ascania and a titular Count of Weimar-Orlamünde.

He was the son of Count Herman II and his wife, Beatrix of Andechs-Merania.

On 29 December 1279, Otto III founded Himmelskron Abbey.

He died in June 1285, and was buried in the collegiate church of the abbey.