Polystyrene/poly(ethylene oxide) heteroarm star copolymers (i.e., star-shaped polymers consisting of a central poly(divinylbenzene) core bearing an equal number of short polystyrene and long poly(ethylene oxide) arms, PS10PEO10) were synthesized by anionic polymerization, and their phase behavior was investigated in aqueous solutions as well as in water-oil solvent mixtures. Because of their amphiphilic character and despite their star architecture, these polymeric species self-assemble under equilibrium conditions into lyotropic liquid crystalline structures.