The Thermal Field-Flow fractionation (TFFF) method was used to determine the elution volume of a series of star branched polystyrene having different number of arms but the same molecular weight and polystyrene standards with narrow distribution whose molecular weight ranged from 5.0×104 to 86×104. Results were obstained by measuring at two) temperature differentials (△T=30℃ and △T=50℃) in THF. These star branched samples were also measured by means of GPC method. Comparison of the Vr-M relationship obtained from TFFF and GPC showed that the displacement of Vr-M curves for star branched and linear polystyrene is larger in TFFF than in GPC.The difference is caused by the different mechanism of separation for these two methods. As the controlling factor is the hydrodynamic volume of the polymer chain in solution for GPC

it is the diffusion coefficient of polymer molecules for TFFF.The experimen-tal results indicate that the influence of variance of chain structure on diffusion coef-ficient is stronger than that on the hydrodynamic volume and that TFFF technique maybe used as a method for characterizing branching oof polymer molecules. For this purpose a proper theroetical model and more accurate experiments are needed.