The formation of vesicles based on the self-assembly of amphiphilic poly(butadiene)-b-poly(ethylene oxide) (PB130-b-PEO66) block copolymer in water has been studied using THF as co-solvent. To obtain a highly controlled mixing process for the polymer/THF- and the water-phase, we employed micro mixers with different mixing geometries. The high impact of this preparation method on the self-assembling process was verified by TEM and DLS characterization of the obtained structures. Spherical micelles, vesicles and worm-like micelles were found depending on the parameters of mixing. By additional parameter adjustment in the vesicle regime, the size of the assembled vesicles was controlled between 45 and 100 nm. This demonstrates the continuous preparation of narrowly distributed vesicle structures with controlled sizes. (C) 2012 Elsevier Ltd. All rights reserved.