We develop a new method to prepare block copolymer vesicles with high loading capacity of drugs which can then be released in a controlled manner. The block copolymers, including PS-b-PAA, PS-b-PEO, and biocompatible PCL-b-PEO, can directly self-assemble into vesicles in aspirin and encapsulate aspirin by solvent annealing with ethanol which imparts mobility to the originally solid block copolymers and aspirin molecules. Aspirin associates with the hydrophilic blocks after premixing, firstly leading to the formation of bilayer structures. During solvent annealing, the bilayers are wrapped into vesicles to enclose aspirin that fills the cores of the vesicles. The interactions between block copolymers and aspirin were probed by FT-IR, and the formation of aspirin-loaded vesicles were confirmed by transmission electron microscopy and dynamic light scattering. The loading content of aspirin in the extracted vesicles is 59 +/- 5%, higher than that of conventional vesicles formed in liquid systems with dilute drugs. The release rate and final release amount of aspirin from vesicles in aqueous solutions can be controlled by addition of different amount of n-dioxane or by changing pH values. (C) 2017 Elsevier Ltd. All rights reserved.