The surface interactions between xanthene (XN) dyes, including rhodamine B, rhodamine 3B, rhodamine 19, rhodamine 6G, rhodamine 110, and rhodamine 123, and tungsten(VI) oxide (WO3) colloid particles were investigated. These XN dyes were strongly adsorbed as a monolayer onto the WO3 surface via the electrostatic interaction between their peripheral cationic amino substituents and negatively surface-charged WO3 colloid particles, and most of the ones adsorbed eventually formed stable pi-stacked dimers. The geometry of dimers formed on the WO3 colloid surface is discussed on the basis of the molecular exciton theory framework. Cationic XN dyes formed the approximately ideal face-to-face H-dimers on the WO3 colloid surface, whereas zwitterionic ones had a higher tendency to form the oblique J-dimers. Additionally, we have experimentally demonstrated the possibility of pH-induced switching between H- and J-aggregation modes of the XN dye's dimers formed on the WO3 colloid surface. The findings lead to a better understanding of organic dye's adsorption/aggregation behaviors on the metal oxide surface.