Tellurous acid is an inorganic compound with the formula H₂TeO₃. It is the oxoacid of tellurium(IV). The compound is not well characterized. An alternative way of writing its formula is (HO)₂TeO. In principle, tellurous acid would form by treatment of tellurium dioxide with water, i.e. hydrolysis. The related conjugate base is well known in the form of several salts such as potassium acid tellurite, KHTeO₃.