In this work, self-assembled poly(butadiene)-b-poly(ethylene oxide) (PB-PEO) polymersomes (polymer vesicles) and worm micelles were evaluated as paclitaxel carriers. Paclitaxel was successfully incorporated into PB-PEO polymersomes and worm micelles. The loading capacity of paclitaxel inside PB-PEO colloids ranged from 6.7% to 13.7% w/w, depending on the morphology of copolymer colloids and the molecular weight of diblock copolymer. Paclitaxel loaded OB4 (PB219-PEO121) polymersome formulations were colloidally stable for 4 months at 4 degrees C and exhibited slow steady release of paclitaxel over a 5 week period at 37 degrees C. Evaluation of the in vitro cytotoxicity of paclitaxel-polymersome formulations showed that the ability of paclitaxel-loaded polymersomes to inhibit proliferation of MCF-7 human breast cancer cells was less compared to paclitaxel alone. By increasing the concentration of paclitaxel in polymersomes from 0.02 to 0.2 mu g/mL, paclitaxel-polymersome formulations showed comparable activity in inhibiting the growth of MCF-7 cells. Taken together, these results demonstrate that paclitaxel-polymersomes have desirable restrained release profile and exhibit long-term stability.