Hyperbranched polyurethane (HP) and its linear analog (LPU) were studied by size exclusion chromatography (SEC), utilizing a combination of refractive index (RI), right angle light scattering (RALLS), and differential viscosity (DV) detectors. The relationships between retention volume (V-e), intrinsic viscosity (eta), radius of gyration (R.), and the molecular structure were investigated. It was shown that the hyper-branched polyurethane had lower V-e, eta, and R-g than its linear analog when they had the same molecular weight. The branching parameter g and g' were calculated.