The Treaty of Dubysa or Treaty of Dubissa () consisted of three legal acts formulated on 31 October 1382 between Jogaila, Grand Duke of Lithuania, with his brother Skirgaila and Konrad von Wallenrode, Marshal of the Teutonic Knights. During the Lithuanian Civil War (1381–1384), Teutonic Knights helped Jogaila and Skirgaila to defeat his uncle Kęstutis with his son Vytautas. Trying to realize promises given by Jogaila during the war, Teutonic Knights organized the negotiations for the treaty. The acts were signed after six days of negotiations on an island in the mouth of the Dubysa River. The treaty was never ratified and never came into effect. The war resumed in summer 1383.