Different amphiphilic triblock copolymers of n-butyl methacrylate (BMA) and 2-methacryloyloxyethyltrimethyl ammonium iodide were prepared by the reaction of precursor polymer and iodomethane. The precursor polymers were obtained by Group-Transfer Polymerization (GTP) of BMA with 2-(dimethylamino)ethyl methacrylate (DMAEMA) using a difunctional initiator at room temperature. Their molecular weight and composition could be controlled by regulating the monomer to initiator ratio and the feed ratio of two monomers. From quantitative quaternization of poly(DMAEMA) segments of precusor polymers by iodomethane, the target polymers were prepared. These amphiphilic triblock copolymers exhibited excellent surface activity and lowered the surface tension of their aqueous solutions. The lowest surface tension (gamma) value reached to 27.4 dyn/cm.