The adsorption and the interactions of water-soluble chitosan (DD = 50%) with main components of reed pulp suspensions were investigated with phenol/sulfuric acid spectrophotometry, microelctrophoresis, and retention/drainage methods. The results showed that the Zeta potential of peroxide bleached reed kraft pulp transformed from negative to zero and then to positive because of the adsorption of water-soluble chitosan. Nonelectrostatic forces (hydrogen bonding, Van der Waals force) existed between the fibers and water-soluble chitosan; electrostatic force existed between cellulose fines and water-soluble chitosan. The experimental results showed that the fines existed in pulp suspension would aggregate upon the addition of water-soluble chitosan. The degree of flocculation was affected by the type of cellulose substrates, the electrolyte concentration and pH in the background. With the increase of NaCl concentration, the flocculation performance of water-soluble chitosan decreased slightly for unwashed pulp, whereas the flocculation efficiency of water-soluble chitosan decreased significantly for fine suspension. These adsorption and flocculation resulted in excellent drainage performance of reed pulp, for example, the (0)SR of cellulosic pulp was reduced by about 39 or 18% at C(NaCl) = 0 mol/L, at pH 5 or pH 7, respectively. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 2606-2613, 2011