A series of chitosan-graft-polyacrylamide copolymers have been prepared as flocculants for waste water treatment. The results indicated that the grafting ratio was one of the key factors for the flocculating effects. The copolymers with various grafting ratios showed different flocculating properties. To observe every detail of this effect, the specific refractive index increment measurement (SWIM) method was used to determine the grafting ratio at the beginning of this study. Interestingly, it was found that as the grafting ratio increased, the flocculating effect increased until it reached its maximum point. At that point, it decreased. This result was discussed in terms of the cooperative effects of the charge neutralization and bridging flocculating mechanisms. A structure model of chitosan-g-polyacrylamide copolymer flocculants has been proposed. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 1876-1882, 2010