Yakin Valmy ya kasance babban rikici a yakin juyin juya halin Faransa, wanda aka yi a ranar 20 ga Satumba, 1792, tsakanin sojojin juyin juya hali na Faransa da kuma sojojin Prussian masu mamaye. Yakin da ya gudana a kusa da kauyen Valmy da ke arewa maso gabashin Faransa, ya haifar da nasara a Faransa, kuma ana daukar wani sauyi a yakin. An ba shi sunan ƙauyen Valmy inda aka yi yaƙi da shi.