A novel amphiphilic biodegradable poly(ethylene glycol)-poly(2-methyl-2-carboxyl-propylene carbonate) (MPEG-PMBC) block copolymer was successfully synthesized by ring-opening polymerization (ROP) of 2-methyl-2-carboxyl-propylene carbonate (MBC) with MPEG as a macroinitiator. C-13 NMR and GPC confirmed its structure. It could self-assemble into micelles in aqueous solution with the critical micelle concentration (cmc) as low as similar to 10(-3) g/l. The cmc decreased with increasing PMBC content. DLS analyses of the MPEG-PMBC micelles revealed their size of less than 100 nm and narrow size distribution. The micelle size depends much on the copolymer composition and micelle preparation conditions. The morphology of micelle observed by ESEM is spherical. The obtained polymeric micelles are expected to be used as biomedical materials such as drug delivery vehicles. (c) 2005 Elsevier Ltd. All rights reserved.