Poly (styrene-b-isoprene) (PS-b-PI) star-block copolymers were studied by triple detector size exclusion chromatography (SEC3), utilizing a combination of refractive index (RI), right angle light scattering (RALLS), and differential viscosity (DV) detectors. The relationships between the number of arms, the composition, and molecular size of the star polymers were investigated. The effect of the number of arms of the star polymer on elution behavior was established and compared to a linear polystyrene calibration curve. It was found that universal calibration was valid for star polymers having up to 32 arms. The branching parameters (g and g') were calculated from intrinsic viscosity and radius of gyration data. The results indicate that, in addition to molecular weight determinations, much useful conformational information on star-block copolymers can be obtained from SEC3. The technique is an especially useful tool for characterizing branched copolymers, which are difficult to characterize by conventional SEC.