The steady flow and dynamic viscoelastic properties of disperse systems consisting of polystyrene copolymer particles of different sizes in polystyrene solutions were measured by means of rotating cylinder type rheometers over wide ranges of temperature, rate of shear, and frequency. The yield values, evaluated by use of the modified Casson equation for disperse systems, were found to be independent of temperature. Time‐temperature superposition was applied to the flow curves and the frequency dependence curves of the dynamic properties, giving identical shift factors which obeyed the WLF type equation and were almost independent of the size and content of the particles. The yield value increased with increasing particle content and polymer concentration in the disperse medium. The smaller the particle size, the larger the yield value. The frequency dependence curves of the storage shear modulus G′ and the loss modulus G″ showed second plateaus lower than the rubbery plateau at lower frequencies. The correlation between the yield value and the complex shear stress is discussed.