This paper reports on a new method to analyze the adsorbed structure of an anionic polymer dispersant on an alumina powder surface in dense suspension with different additive content by using an atomic force microscope (AFM). Anionic polymer dispersants were adsorbed on both the polished surface of a thin piece of sintered alumina and the surface of alumina powders in dense alumina suspension. After separation of the thin alumina piece and a clear layer from the dense suspension achieved by centrifugal sedimentation method, the adsorbed structure and electrosteric interactions of polymer dispersion on the polished surface of the sintered alumina were examined by using AFM. At an optimum additive content, which was obtained at the minimum viscosity of suspension, the maximum repulsive force was observed. At this point the adhesive force between the alumina surface and the tip of the AFM cantilever almost disappeared. With an excess addition of polymer dispersant, a decrease of electrosteric repulsion force was observed because the free polymers in solution compressed the adsorbed polymers. Both the decrease of electrosteric repulsion and the re-bridging of the dispersant between particles caused an increase of the suspension viscosity.