The Thermal Field-Flow Fractionation (TFFF) method was used to determine the elution volumeof a series of star branched polystyrene having different number of arms but the same arm molecularweigh and polystyrene standards with narrow distribution whose molecular weight ranged from5.0×104 to 8.6×105. Results were obtained by measuring at two temperature difference (△T=30℃and △T=50℃ in THF. The same star branched samples were measured by means of GPC method.Comparison of Vr-M relationships obtained from TFFF and GPC showed that the displacement of Vr-M curves for star and linear polystyrene is larger than that in GPC.This difference is caused by the entirely different mechanism of separation for these two methods.As the controlling factor is hydrodynamic volume of the polymer chain in solution for GPC

it is the diffusion coefficient of polymer molecules for TFFF.The experimental results indicate that the influence of variance of chain structure on diffusion coefficient is stronger than that on the hydrodynamic volume and that TFFF tech-nique may be used as a method for characterizing branching of polymer molecules.For this purpose a proper theoretical model and more accurate experiments are needed.