Abstract: To investigate the mechanisms of how nanobubbles enhance the flotation separation performance of galena from pyrite, the effects of nanobubbles on the surface properties of galena and pyrite and the interactions between mineral particles and air bubbles were examined in this study. Various analytical techniques, including focused beam reflectance measurement (FBRM), three-phase contact line (TPCL) analysis, atomic force microscopy (AFM), and contact angle measurement, were employed. It has been demonstrated that nanobubbles significantly enhanced the flotation recovery of galena and its flotation selectivity from pyrite, as compared to the conventional flotation process. The preferential formation of nanobubbles on the galena surface, which is more hydrophobic than pyrite surface, further increased the surface hydrophobicity and agglomeration of galena particles. The introduction of nanobubbles into the flotation system also increased in the maximum TPCL length and detachment length between the galena surface and bubbles, contributing to the enhanced flotation efficiency.