Tellurous acid is an inorganic compound with the formula H2TeO3.

In principle, tellurous acid would form by treatment of tellurium dioxide with water, that is by hydrolysis.

The related conjugate base is well known in the form of several salts such as potassium hydrogen tellurite, KHTeO3.

Oxidation of its aqueous solution with hydrogen peroxide gives the tellurate ion.

It is usually prepared as an aqueous solution where it acts as a weak acid.