New carboxymethylcellulose-based graft copolymers with an amphoteric character were synthesized by grafting 2-(dimethylamino)ethyl methacrylate onto carboxymethylcellulose using a persulfate-initiated solution polymerization technique. Their multifunctional characteristics as an oilfield drilling-mud additive were investigated with respect to shale inhibition, viscosity building, and filtration control. It was shown that the graft copolymer with an appropriate grafting extent is characteristic of both good shale inhibition and mud properties and may overcome the limitations inherent; in commonly used anionic and cationic polymeric additives.