This study investigates how changes in the surface properties of three representative sulfide minerals (galena, sphalerite and chalcopyrite) affect their floatability in the presence of an oxidizing agent (H2O2). Tests were conducted at four molar ratios of H2O2: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 floatability 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 floatability was evaluated by a microflotation method. At the acidic initial pH, galena most sensitively reacted with H2O2, followed by chalcopyrite and sphalerite, whereas at pH 10, the reactivity differences were insignificant. H2O2 addition changed the sulfide species (initially present on the mineral surface) to sulfate or hydroxyl species, and decreased the mineral floatability. To investigate the surface property that mainly reduced the mineral floatability in the presence of H2O2, we measured the zeta potentials and contact angles, which are closely associated with the electrostatic and hydrophobic forces, respectively. The floatability depended on the contact angle after the H2O2 addition, implying that the floatability was mainly reduced through oxidation reactions, which increased the hydrophilicity of the mineral surface.