The synthesis and aggregation behaviour in aqueous media of novel amphiphilic poly(ethylene oxide)- block-poly(n-butyl acrylate)-block-poly(acrylic acid) (PEO¿PnBA¿PAA) triblock terpolymers were studied. Terpolymers composed of two highly asymmetric hydrophilic PEO (113 monomer units) and PAA (10¿17 units) blocks, and a longer soft hydrophobic PnBA block (163 or 223 units) were synthesized by atom transfer radical polymerisation (ATRP) of n-butyl acrylate and tert-butyl acrylate (tBA), followed by selective hydrolysis of the PtBA blocks. These terpolymers are not directly soluble in water but form defined spherical micelles by employing the dialysis method as confirmed by dynamic light scattering (DLS) and cryogenic transmission microscopy (cryo-TEM). Based on terpolymer architecture and composition, a three-layered micellar structure comprising a PnBA core, a PEO/PAA middle layer, and a PEO outer layer is suggested. The micelles do not dissociate to very low concentrations and, therefore, are promising candidates for long-circulating drug delivery systems. Further, as evidenced by high-performance liquid chromatography (HPLC), the micelles can load and release, without burst effect, the hydrophobic drug paclitaxel.