三聚磷酸钠，化学式Na₅P₃O₁₀。

三聚磷酸钠是一种白色粉末，易溶于水，水溶液呈碱性，1％水溶液pH为9.7。有两种晶形，α型（高温型）和β型（低温型），两者化学性质相同，均可得到相同的水溶液和结晶水合物，不过热稳定性、溶解度、溶解时水合热量以及吸湿性均不同。它在水中会逐渐水解为正磷酸盐。有良好的配位能力，可与钙、镁、铁等金属离子络合。也是一种无机表面活性剂。

Sodium triphosphate (STP), also sodium tripolyphosphate (STPP), or tripolyphosphate (TPP),) is an inorganic compound with formula Na₅P₃O₁₀. It is the sodium salt of the polyphosphate penta-anion, which is the conjugate base of triphosphoric acid. It is produced on a large scale as a component of many domestic and industrial products, especially detergents. Environmental problems associated with eutrophication are attributed to its widespread use.