Abstract: The existence of Ca-oleate (Ca(OL)₂) colloid and its effect on flotation during the flotation of scheelite, fluorite and calcite with sodium oleate were studied. Solution chemistry showed that the dissolved calcium ions from the three calcium-containing minerals can react with oleate anions to form Ca(OL)₂ colloids, which exist and function as the main components in solutions under alkaline conditions. The pure minerals tests showed that the collection ability of Ca(OL)₂ colloid for scheelite and fluorite was stronger than that of sodium oleate, and for calcite was weaker than that of sodium oleate. The difference in the surface hydrophobicity of the three minerals after Ca(OL)₂ colloid adsorption increased. The surface hydrophobicity of scheelite and fluorite was stronger than that of sodium oleate, while the surface hydrophobicity of calcite was weaker than that of sodium oleate. Chemical adsorption of Ca(OL)₂ colloids occurred on the surface of scheelite. On the surface of fluorite and calcite, it was mainly chemical adsorption, and there was also electrostatic adsorption when pH < 9.0. In the flotation process of calcium-containing minerals with sodium oleate, in addition to the direct action of oleic acid anions on the surface of minerals, there was another important action path: calcium ions and oleic acid anions first generate Ca(OL)₂ colloids in solution, and Ca(OL)₂ colloids migrated to the mineral surface in solution and adsorbed on the minerals surface.