Sodium Hexametaphosphate or SHMP is a hexamer of composition (NaPO3)6. Sodium Hexametaphosphate of commerce is typically a mixture of polymeric metaphosphates, of which the hexamer is one, and is usually the compound referred to by this name. It is more correctly termed sodium polymetaphosphate. It is prepared by melting monosodium orthophosphate, followed by rapid cooling. SHMP hydrolyzes in aqueous solution, particularly under acidic conditions, to sodium trimetaphosphate and sodium orthophosphate.

Sodium Hexametaphosphate is used as a sequestrant and has applications with in a wide variety of industries, including as a food additive in which it is used under the E number E452i. Sodium carbonate is sometimes added to Sodium Hexametaphosphate to raise the pH to 8.0-8.6, which produces a number of Sodium Hexametaphosphate products used for water softening and detergents. Also used as a dispersing agent to break down clay and other soil types.

One of the lesser-known uses for Sodium Hexametaphosphate is as a deflocculant in the making of terra sigillata, a ceramic technique using a fine particled slip. The Sodium Hexametaphosphate causes the heavy particles in the slip to drop to the bottom allowing the fine particles to be siphoned off and applied to a green ware ceramic surface.