A novel GPC calculation method has been developed for characterizing star-shaped styrene-butadiene block copolymers (SBS). This method enables us to determine the degree of branching (number of arms per molecule) of the synthesized polymer without the need of a priori measurement of the true molecular weights of the SBS star polymer and its linear polymeric arm. To illustrate the simplicity of this method, nearly monodispersed three-arm and four-arm model star polymers have been purposely synthesized by linking living diblock polymeric arms of the polystyrene-block-polybutadiene type with silicon tetrachloride as the multifunctional linking agent. The good agreement between the degree of branching calculated from the GPC chromatogram and that actually measured by MALL (multiple angle laser light scattering) has corroborated the validity of the calculation method.