The hydrophobically modified water-soluble graft copolymer of sodium carboxymethylcellulose with acrylamide and dimethyloctyl(2-methacryloxyethyl)ammonium bromide has been synthesized using potassium persulfate and dimethylaminoethyl methacrylate as initiators in aqueous solution. The structure and composition of the graft copolymer were characterized by infrared spectrum and elementary analysis. Molecular weight was determined by gel permeation chromatography. The solubility and viscosity of the graft copolymers in aqueous solution were investigated, as a function of copolymer concentration, added salt, temperature, shear rate, and surfactant. In addition, the intermolecular hydrophobic association in aqueous solutions in the presence of added salt and surfactant was demonstrated through the retention time from gel permeation chromatography measurement.