This study investigates how changes in the surface properties of three representative sul de minerals (galena, sphalerite and chalcopyrite) affect their oatability in the presence of an oxidizing agent (H 2 O 2 ). Tests were conducted at four molar ratios of H 2 O 2 :mineral (0, 0.5, 1.0, and 2.0). To better capture the effect of surface oxidation, the tests were conducted at both acid and basic conditions (i.e., pH = 3 and 10). In all surface property and oatability evaluations, the pH and Eh were equilibrated. The surface properties were evaluated by X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential measurements and contact angle analyses. The oatability was evaluated by a micro otation method. At the acidic initial pH, galena most sensitively reacted with H 2 O 2 , followed by chalcopyrite and sphalerite, whereas at pH 10, the reactivity differences were insigni cant. H 2 O 2 addition changed the sul de species (initially present on the mineral surface) to sulfate or hydroxyl species, and decreased the mineral oatability. To investigate the surface property that mainly reduced the mineral oatability in the presence of H 2 O 2 , we measured the zeta potentials and contact angles, which are closely associated with the electrostatic and hydrophobic forces, respectively. The oatability depended on the contact angle after the H 2 O 2 addition, implying that the oatability was mainly reduced through oxidation reactions, which increased the hydrophilicity of the mineral surface.