Sodium iodide is very soluble in water and some organic solvents. It is sensitive to air, moisture and light, and solid NaI turns brown on exposure to air or light, due to formation of iodine fumes. It also reacts violently with strong oxidants, strong acids and bromine trihalides, producing iodine.

Sodium iodide is commonly used as a dietary iodine supplement and included in table salt (NaCl). It is used to treat and prevent iodine deficiency. Sodium iodide is also used as a reagent in organic synthesis to prepare various alkyl iodides.