Propionic acid (PA) also known as propanoic acid is a short chain fatty acid mainly used as food preservative. It is one of the main metabolic end product formed during the fermentation of undigested food in the colon by the microbiota. Its manufacture by glycerol/glucose co-fermentation using Propionibacterium acidipropionici has been reported. Crystal structure study reveals that PA crystals are monoclinic with space group P2₁/c.

Propionic acid (PA) is a naturally occurring carboxylic acid, which in its pure state exists as a colorless corrosive liquid with an unpleasant odor. It is miscible in water. Industrially it is produced by hydrocarboxylation of ethylene in presence nickel carbonyl as a catalyst. PA has been found to reduce food intake, lower the fatty acids content in plasma and liver, might improve tissue insulin sensitivity and exerts immunosuppressive actions. Propionic acid is an excellent raw material as it is stable, cheap and safe and can even be used as a food additive.

Propionic acid may be used to alter limestone in order to increase its ability of CO₂ uptake.