Ermsdorf (Luxembourgish: Iermsdref) is a village and former commune in eastern Luxembourg. It is part of the canton of Diekirch, which is part of the district of Diekirch.

As of 2024, the village of Ermsdorf, which lies in the south of the commune, has a population of 466.

In 2011, Ermsdorf merged with Medernach to become the commune of Vallée de l'Ernz.

The former commune consisted of the villages:

• Eppeldorf
• Ermsdorf
• Folkendeng
• Keiwelbach
• Stegen
• Backesmillen (lieu-dit)
• Bricherheck (lieu-dit)
• Bricherhaff (lieu-dit)
• Gilcher (lieu-dit)
• Hessemillen (lieu-dit)
• Hoossebierg (lieu-dit)
• Moderhaff (lieu-dit)
• Neimillen (lieu-dit)
• Reisermillen (lieu-dit)
• Spierberich (lieu-dit)
• Webeschhaff (lieu-dit)