We report the characterization of polystyrene by temperature-gradient interaction chromatography (TGIC) with on-line light-scattering (LS) detection. Since a binary mixture eluent, CH2Cl2/CH3CN (57/43, v/v), was employed in TGIC, a systematic deviation in apparent molecular weight due to preferential sorption was observed. After an appropriate correction, however, correct molecular weights could be obtained. Second virial coefficients obtained from light-scattering measurement showed that the TGIC separation condition is very close to the Theta condition. With the TGIC/LS setup, analysis of an unfractionated six-arm star polystyrene was carried out. The resolution of TGIC was high enough to resolve all the polymer molecules having one to six arms. Comparison of LS detection results with the results obtained by calibration with linear PS standards reveals that elution in TGIC is far more sensitive to molecular weight alone. Thus it provides an excellent route to separating polymer molecules of similar hydrodynamic volume but differing molecular weight.