Sedimentation of small particles through liquid has been widely utilized to measure easily the size of the particles. Conserning this, experiments were carried out both for the case of a single particle falling through liquids and for the case where particles constitute a dispersion system and fall through liquids, and the following are clarified : (1) Drag coefficients measured on a single particle are approximately expressed with Stokes' law for creeping flow motion. (2) With sedimentation of dispersed particles, the falling velocity is in some cases abnormally low, though the concentration of the dispersion system used is hitherto thought to be too low to induce interaction among the suspended particles. (3) The abnomally low sedimentation speed is possibly due to the interaction among the suspended particles which are surrounded with electric double layers. (4) To suppress the occurrence of the abnomally low sedimentation speed and no measure the nearly correct size of particles, it is effective to add NaCl of the order of 1 mol/1 to the water of dispersion medium.