A new amphiphilic biodegradable methoxypolyethylene glycol/poly(D,L-lactide)/poly(ethyl ethylene phosphate) (MPEG-b-PEA-b-PEEP) block copolymer was synthesized by ring-opening polymerization of ethyl ethylene phosphate (EEP) with methoxypolyethylene glycol/poly(D,L-lactide) (MPEG-b-PEA) as a macroinitiator, which was prepared by ring-opening polymerization of D,L-lactide (LA) initiated by methoxypolyethylene glycol (MPEG) using stannous octoate as catalyst. The structures of the block copolymers were confirmed by IR. (1)H NMR and GPC analysis. Fluorescence measurements were applied to determine the critical micelle concentration (CMC) of the copolymer micelle solutions. The diameter and the distribution of micelles were characterized by dynamic light scattering (DLS) and the shape was perceived using transmission electron microscopy (TEM). The results prove that the copolymers can self-assemble into nano-micelles in aqueous solutions. The CMC of the copolymer solutions increased and the size of the micelles reduced with increasing of the proportion of PEEP segments. TEM images demonstrate that all micelles are spherical. (C) 2011 Elsevier Ltd. All rights reserved.