The rheological study of dispersions of poly(methyl methacrylate) particles stabilized in decane by a steric stabilizer, polystyrene-block-poly(ethylene-co-propylene) diblock copolymer, revealed an extremely high apparent viscosity at low shear rates or even the yield stress at a relatively low volume fraction of particles (similar to 0.1). This behavior is due to highly interacting stabilizer macromolecules anchored to the particle surface. As the concentration of poly(methyl methacrylate) is further increased. the volume fraction of particles also increases, the particle diameter grows, the number of particles is reduced and the viscosity of the dispersion falls.