Heteroarm star copolymers, i.e. star-shaped polymers bearing A and B pure arms (type A(n)B(n)) were synthesized by anionic polymerization and their hydrodynamic properties in a common good solvent were investigated by means of size exclusion chromatography. The proposed method allows the study of the evolution of the hydrodynamic dimensions of the heteroarm star copolymers as the second generation of the arms is growing from the cores. Different growth rates of the A(n)B(n) star size were observed which are influenced by three factors: the number of arms, the ratio of the size of the chemically different arms and the interactions between the unlike segments. The last factor is affected significantly by the selectivity of the solvent.