Biodegradable amphiphilic ABC Y-shaped triblock copolymer (MPBC) containing PEG, PBLA, and PCL segments was synthesized via the combination of enzymatic ring-opening polymerization (ROP) of epsilon-caprolactone, ROP of BLA-N-carboxyanhydride and click chemistry, where PEG, PBLA, and PCL are poly(ethylene glycol), poly(benzyl-l-aspartate), and polycaprolactone, respectively. Propynylamine was employed as ROP initiator for the preparation of alkynyl-terminated PBLA and methyloxy-PEG with hydroxyl and azide groups at the chain-end was used as enzymatic ROP initiator for synthesis of monoazido-midfunctionalized block copolymer mPEG-b-PCL. The subsequent click reaction led to the formation of Y-shaped asymmetric heteroarm terpolymer MPBC. The polymer structures were characterized by different analyses. The MPBC terpolymer self-assembled into micelles and physically encapsulated drug doxorubicin (DOX) to form DOX-loaded micelles, which showed good stability and slow drug release. In vitro cytotoxicity study indicated that the MPBC micelles were nontoxic and the DOX-loaded micelles displayed obvious anticancer activity similar to free DOX against HeLa cells. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3346-3355