The aim of this study was to determine the effect of particle size on the oxidation and flotation behavior of galena particles. Coarse (-0.074+0.038 mm), intermediate (-0.038+0.025 mm) and fine (-0.025 mm) galena particles were used in this study. Dissolution tests demonstrated that the amount of oxidation products increased with the decrease of particle sizes. The surface oxidization of galena was the greatest at pH 7.3, followed by pH 12 and 9, which were consist with the result of XPS. The micro-flotation results indicated that the effect of pH on the flotation recovery of galena enhanced with the reduction of particle sizes. The decreasing of particle sizes increases both the sorption rate of collector and the dissolution of galena, while the generation of hydrophilic product caused by dissolution is dominant, rendering the mineral hydrophilic. This study shows the differences in the surface oxidation and flotation behavior of different size fractions of galena particles. To promote the flotation recovery of the fine size fraction of galena particles, alleviating their oxidation is the key.