It is the aim of this paper to discuss the physical imports of the sieve analysis, with respect to the sedimentation methods.In view of the theory of sieving process by proposed Fagerholt, that the cut size of the sieved residue obtained in the time (t) can be determined as the average particle size of the fraction in a continued sieving process under the same condition from the time (t) to the time (3t), it is inferred from experimental results, that:1. The effective opening of the sieve depends on the residue on that sieve, and it is represented in Eq. (9).2. When the cumulative residue retained on each sieve are plotted against the effective opening line, for example Fig. 5, 6 and 7, the particle size distribution line is independent of the error of the opening of the sieve or any other sieving condition.3. The particle size distribution obtained by sieve analysis is related to the diameter of equivalent spheres having the same volume of particles of the cut size. In the case of spherical particles, it is approximately equal to the opening of the sieve, and in the irregularly shaped particles, it is somewhat greater than the opening of the sieve, Eq. (11).4. The particle size distributions obtained by the sedimentation methods, whether the particles are spherical or irregular, corresponds to the effective opening of the sieve for spherical particles.