三碘化磷是一种无机化合物，化学式PI₃。可以和水剧烈反应。

三碘化磷可以和水剧烈反应，产生亚磷酸和碘化氢，产物中也有少量杂质如磷化氢和含有P-P键的化合物。

三碘化磷也是个强还原剂和脱氧剂。它可以还原亚砜到硫醚，即使在-78℃也可以完成反应。

Phosphorus triiodide (PI₃) is an unstable red solid which reacts violently with water. It is a common misconception that PI₃ is too unstable to be stored; it is, in fact, commercially available. It is widely used in organic chemistry for converting alcohols to alkyl iodides. It is also a powerful reducing agent. Note that phosphorus also forms a lower iodide, P₂I₄, but the existence of PI₅ is doubtful at room temperature.