The structural change during particle dispersion process of highly concentrated slurries of PMMA and graphite particles was investigated in terms of viscoelasticity. PMMA particles having weak interaction are easy to be dispersed, and a higher shear rate was preferable for stable dispersion. In contrast, aggregated graphite particles generate sedimentation layer. Therefore, non-uniform slurry was obtained at the lowest shear rate, while the formation of network of aggregated graphite particles resulted in a highly viscoelastic slurry when dispersing at higher shear rates. Additionally, it was considered that the particle dispersion is completed at the shear rate, when the loss moduli of slurry and dispersing medium showed the same frequency dependence.