In this study, a series of amphiphilic AB(2)-type miktoarm star block copolymers consisting of hydrophobic poly(L-lactide) (PLLA) as a A arm and hydrophilic poly(N-acryloylmorpholine) (PNAM) as two B arms were synthesized via the combination of ring opening polymerization and xanthate-mediated reversible addition-fragmentation chain transfer polymerization. Resultant polymers were analyzed by H-1 NMR spectroscopy and gel permeation chromatography. Aggregation properties of the amphiphilic miktoarm star block copolymers were studied by fluorescence spectroscopy, transmission electron microscopy and dynamic light scattering. Doxorubicin (DOX) was successfully loaded into the miktoarm star block copolymer micelles and the DLC and DLE of the DOX-loaded micelles increased (9.4 to 13.6% and 55.6 to 78.7%) with an increase in the hydrophilic PNAM chain length of the miktoarm star block copolymer. The result revealed that DOX release was enhanced as the pH reduced from 7.4 to 6.4 and the rate of release slightly increased with increasing the PNAM hydrophilic chain length of the micelles.