The solubilization of a poorly water-soluble antiepileptic drug, carbamazepine (CBZ), in a series of micelle-forming PEO–PPO–PEO block copolymers with combinations of blocks having different molecular weight was studied. The drug solubility and micelle–water partition coefficient (P) were determined using UV–vis spectroscopy. Dynamic light scattering on copolymer solutions was used to measure size and polydispersity of nanoaggregates. Solubilization of carbamezapine increased with the rise in temperature and concentration of block copolymers, but no significant increase was observed with added salt (NaCl). The solubilization is also discussed from a thermodynamics viewpoint, by considering the standard free energy of solubilization (ΔG°).