The settling behavior of quartz using chitosan as flocculant has been studied and the mechanism has been discussed. The sedimentation results show that pH has an influence on the settling behavior of quartz particles and the sedimentation velocity is more quickly at acidic pH range. Chitosan is a useful flocculant for the settling of quartz but its flocculation effect is influenced greatly by pH. The sedimentation velocity of quartz is quickly and the volume of sediment is large when chitosan was added at pH 9. The reason is that chitosan is only sparingly soluble in water at pH 9, thus the adsorption amount is large and produce strongly flocculation effect. However, when the pH was changed from 9 to 3, the adsorbed chitosan desorption from quartz surface and the flocculation effect disappeared. The flocs were disorganized to the particles and the sediment can be consolidated to significantly higher densities.