Tetraboric acid or pyroboric acid is a chemical compound with empirical formula H2B4O7.

[2] It is a colourless water-soluble solid formed by the dehydration or polymerization boric acid.

Tetraboric acid is formally the parent acid of the tetraborate anion [B4O7]2−.

Tetraboric acid can be obtained by heating orthoboric acid B(OH)3 above about 170 °C:[3][4]

This inorganic compound–related article is a stub.