This study is concerned with the interaction among fine, medium, and coarse particles in coal flotation. Flotation tests for fine, medium, and coarse particles and the artificial ternary-particle mixtures were executed in a lab flotation cell. Flotation results were evaluated by the modified flotation rate constant (Km) according to the classical first-order flotation model. A parameter called interaction degree was developed to estimate the interaction among fine, medium, and coarse particles. It was observed that the modified flotation rate constant of medium particles was significantly faster than fine and coarse particles. The interaction among of fine, medium, and coarse particles was stronger with a relatively higher proportion of medium particles compared with the proportions of fine and coarse particles. Meanwhile, the gap for flotation rate constant between fast (medium particles) and slow (coarse/fine) fractions narrowed in the ternary-particle mixture flotation.