We have developed the first example of hypervalent iodine(V)-catalyzed regioselective oxidation of phenols to o-quinones. Various phenols could be oxidized to the corresponding o-quinones in good to excellent yields using catalytic amounts of sodium salts of 2-iodobenzenesulfonic acids (pre-IBSes) and stoichiometric amounts of Oxone® as a co-oxidant under mild conditions. The reaction rate of IBS-catalyzed oxidation under nonaqueous conditions was further accelerated in the presence of an inorganic base such as potassium carbonate (K₂CO₃), a phase transfer catalyst such as tetrabutylammonium hydrogen sulfate (nBu₄NHSO₄), and a dehydrating agent such as anhydrous sodium sulfate (Na₂SO₄).