The control of particle dispersion is essential to the fabrication of highly designed ceramics. In this study, a direct observation technique was employed to characterize the heterocoagulation of particles in two-component slurry. TEM observation of solidified slurry composed of alumina and silica particles was attempted to evaluate heterocoagulation. At 10 mass% solid loading, the TEM showed the aggregation of silica with dispersed alumina particles at acidic region. A large scale of aggregation caused by attractive force among alumina and silica particles was observed on the TEM images at neutral region. At basic region, the aggregation of alumina with dispersed silica particles was observed. The measurements of zeta potential and viscosity were conducted to explain the results of the TEM observations.