Potassium nitrate ;is a chemical compound. It is an ionic salt of potassium ions K+ and nitrate ions NO3?, and is, therefore, an alkali metal nitrate. It occurs in nature as a mineral, niter (or niter in the UK). It is a source of nitrogen, and nitrogen was named after niter. Potassium nitrate is one of several nitrogen-containing compounds collectively referred to as saltpeter (or saltpeter in North America).

Major uses of potassium nitrate are in fertilizers, tree stump removal, rocket propellants, and fireworks. It is one of the major constituents of gunpowder (black powder). In processed meats, potassium nitrate reacts with hemoglobin and myoglobin generating a red color. Potassium nitrate has an orthorhombic crystal structure at room temperature, which transforms into a trigonal system at 129 °C (264 °F).

Potassium nitrate is moderately soluble in water, but its solubility increases with temperature. The aqueous solution is almost neutral, exhibiting pH 6.2 at 14 °C (57 °F) ...[More]or a 10% solution of commercial powder. It is not very hygroscopic, absorbing about 0.03% water in 80% relative humidity over 50 days. It is insoluble in alcohol and is not poisonous; it can react explosively with reducing agents, but it is not explosive on its own.