A cationic poly(methyl iodide quaternized styrene-dimethylaminopropylmaleimide) copolymer [poly(MIQSDMAPM)] was synthesized by imidizing styrene-maleic anhydride (SMA) copolymer. Its aqueous solution properties were studied by measurements of reduced viscosity, intrinsic viscosity, and a flocculation test. The reduced viscosity and intrinsic viscosity of this cationic polyelectrolyte were related to the types and concentration of the added salt. "Soft" salt anions were more easily bound to the quaternary ammonium cation (R(4)N(+)) of poly(MIQSDMAPM) than "hard" salt anions. Halide anions are hard anions; consequently, hard cations were more easily attracted to halide anions, and reduced the binding degree of halide anion on the quaternary ammonium group (R(4)N(+)). Some salt ions were observed to strongly attract the quaternary ammonium group of the cationic polymeric side chain and resulted in agglomeration of the polymers. A comparison of various flocculants as to the effect of flocculation was made in this study.