Poly(ethylene glycol) (PEG)-grafted polyaniline (PANi) copolymers were prepared by incorporating a chlorine end-capped methoxy PEG (mPEGCl) of molecular weight of about 2000 onto the leucoemeraldine form of PANi via N-alkylation. The microstructures and compositions of the mPEG-grafted PANi (mPEG-g-PANi) copolymers were characterized by FT-IR, elemental analysis, UV−visible absorption spectroscopy, thermogravimetric (TG) analysis and X-ray photoelectron spectroscopy (XPS). The graft concentration (degree of N-alkylation) can be controlled by adjusting the molar feed ratio of mPEGCl to the number of repeat units of PANi. The mPEG-g-PANi copolymers showed enhanced solubility in common organic solvents and water. The electrical conductivity of the mPEG-g-PANi copolymer film decreased by a factor of 5 at the mPEG graft concentration of 0.05. The mPEG-g-PANi copolymer with a high graft concentration was very effective in preventing platelet adhesion.