The 86th Mixed Brigade (Spanish: 86.ª Brigada Mixta), was a mixed brigade of the Spanish Republican Army in the Spanish Civil War. It was formed in March 1937 with battalions of the Carabineros corps. Until its demise it operated mostly in the Sierra Morena area, at the southern limits of the territory held by the Republic. In January 1938 it was deeply restructured and transformed into an International Brigade having 2,338 international fighters which lasted until 1 October the same year.