A viscometric method has been used to determine the layer thickness of gelatin adsorbed on polystyrene (PS) particles. The layer thickness was found to be 28 nm regardless of the diameter of PS particles, The value of Einstein’s coefficient, cuo for the relative viscosity-volume fraction relation was estimated to be 2.63. Since the PS latex particles were spherical, the value of cuo indicates that even at high shear rates, some aggregation still occurred in the dispersion.