Potassium pentasulfide is the inorganic compound with the formula . It is a red-orange solid that dissolves in water. The salt decomposes rapidly in air.
It is one of several polysulfide salts with the general formula , where M = Li, Na, K and n = 2, 3, 4, 5, 6. The polysulfide salts of potassium and sodium are similar.