We synthesized 200 nm biodegradable nanoparticles (NPs) composed of amphipathic copolymers, L-phenylalanine ethyl ester-grafted poly(gamma-glutamic acid) as drug carriers for atherosclerosis treatment. Paclitaxel (PTX) was successfully loaded on NPs by physical adsorption. The antiproliferative effect of PTX-loaded NPs was clearly observed in umbilical artery smooth muscle cells for at least one week by sustained release of PTX. PTX-loaded NPs are expected to be applicable in the treatment of atherosclerosis.