The authors have studied the Jukuka process from the view-points of soil physics, soil mechanics and chemistry. It is important to recognize the grain size distribution as one of the physical indices. At first we investigated the deflocculating agents and, the initial water contents of samples which dispersed the soil particles best. We used four kinds of deflocculating agents, NaOH, (NaPO3)6, HCl and NH4OH, and the samples presented here were two kinds of volcanic ash sub-soil and two kinds of non-volcanic ash sub-soil. Each of them is composed of soils before land reclaimed to paddy fields, two years later, five years later and ten years later (in case of volcanic ash sub-soil eight years later). In this mechanical analysis, we used the Hydrometer method. Therefore the results obtained are as follows. In the volcanic ash ~oil the dispersion is affected by the initial water contents comparatively and the highest dispersed soil contains about 10-15% more clay than the lowest one, as shown in Fig 1, Fig 3. Concerning Kanto loam (volcanic ash soil), HCl showed the best dispersion before land reclaimed to paddy fields, but(NaPO3)6 Showed best later, as shown in Fig 1. On the other hand in the non-volcanic ash soil the dispersion efficiency does not differ with their initial water contents, and most particles are dispersed by (NaPO3)6 and NaOH, as shown in Fig 5.