Sodium oxide (SOX) is a chemical compound with the formula Na₂O. It is used in ceramics and glasses, though not in a raw form. It is the base anhydride of sodium hydroxide, so when water is added to sodium oxide NaOH is produced.

The alkali metal oxides M₂O (M = Li, Na, K, Rb) crystallise in the antifluorite structure. In this motif the positions of the anions and cations are reversed relative to their positions in CaF₂, with sodium ions tetrahedrally coordinated to 4 oxide ions and oxide cubically coordinated to 8 sodium ions.

Sodium oxide is produced by the reaction of sodium with sodium hydroxide, sodium peroxide, or sodium nitrite:

Most of these reactions rely on the reduction of something by sodium, whether it is hydroxide, peroxide, or nitrite.

Burning sodium in air will produce Na₂O and about 20% sodium peroxide Na₂O₂.

Alternatively, sodium carbonate can be heated to 851 °C, producing carbon dioxide and sodium oxide.

At 208 °C, sodium ascorbate will decompose to furan derivatives and sodium oxide.

Sodium oxide is a significant component of glasses and windows although it is added in the form of "soda" (sodium carbonate). Sodium oxide does not explicitly exist in glasses, since glasses are complex cross-linked polymers. Typically, manufactured glass contains around 15% sodium oxide, 70% silica (silicon dioxide) and 9% lime (calcium oxide). The sodium carbonate "soda" serves as a flux to lower the temperature at which the silica melts. Soda glass has a much lower melting temperature than pure silica, and has slightly higher elasticity. These changes arise because the silicon dioxide and soda react to form sodium silicates of the general formula Na₂[SiO₂]_x[SiO₃].

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