Poly(D,L-lactide-co-glycolide)-poly(ethylene glycol) (PLGA-PEG) diblock copolymers with different compositions were synthesized by ring-opening polymerization of D,L-lactide and glycolide, using monomethoxy PEG as macro-initiator. The resulting copolymers were characterized by nuclear magnetic resonance, gel permeation chromatography, and critical micelle concentration analyses. Self-assembly of the copolymers yielded aggregates of different architectures, including spherical micelles and a mixture of spherical and worm-like micelles with Y-junctions. The self-assembled architecture depends on both the hydrophilic/hydrophobic balance and the molar mass of copolymers. Valsartan, a widely used drug in the treatment of hypertension, was loaded in micelles using a co-solvent evaporation method. High drug-loading content was obtained for worm-like micelles. in vitro drug release was performed at 37°C in pH 7.4 phosphate-buffered saline. An initial burst release is detected in all cases, followed by slower release up to 9 days. The overall release rate is strongly dependent on the degradation of micelles. Copolymers with short PLGA blocks exhibit faster drug release due to faster degradation of micelles, and worm-like micelles present slower drug release as compared to spherical ones. Therefore, PLGA-PEG copolymer micelles with high drug-loading capacity, different architectures, and variable drug release rates could be most attractive for sustained delivery of valsartan.