The dispersed state of particles in high-concentration slurries has a significant effect on the development of the particle packing structure of the powder compact. We observed individual particle motion directly in highly concentrated ceramic slurries under slow flow through confocal laser scanning fluorescent microscopy using transparent slurries. In particular, we focused on particle motion soon after the application of a constant low shear rate. Measurements of the shear stresses indicated that the stress of a 30 vol% slurry gradually increased from 0.018 Pa over time, whereas the stress of a 40 vol% slurry soon reached 0.03 Pa and remained constant. For direct observation, shear stress was applied to the slurry, which was set between two glass plates, by moving one unilateral glass plate at 0.8 mu m/s, to create a shear rate of 0.01 s(-1). The motion of the particles could be observed continuously. In the early stage, particles in the 30 vol% slurry near the moving plate were united as one body and did not alternate positions. Then, a speed incline developed gradually over time. For the 40 vol% case, the particles moved at the same time and together. Increases in the shear stress were caused by increased interaction when the particles were close together.