Tl2O3 + 4H2SO4 → 2H[Tl(SO4)2] + 3H2O
or
Tl2O3 + 4H2SO4 → 2Tl(HSO4)SO4 + 3H2O
Thallium(III) oxide react with sulfuric acid to produce hydrogen disulfatotallate(III) and water. Sulfuric acid - concentrated solution.