Surface-enhanced Raman scattering (SERS) was used to investigate surface segregation in blends of polystyrene (PS) and deuterated polystyrene (DPS) following annealing at temperatures above the upper critical solution temperature (UCST). Blends of PS and DPS were spin-coated onto cleaned silicon wafers from toluene solutions and annealed at temperatures above the UCST. Silver island films were then evaporated onto the blend films, and SERS spectra were obtained. The relative intensities of the bands near 1015 and 975 cm-(1), which were characteristic of PS and DPS, respectively, were used to determine the relative amounts of PS and DPS at the surface of the blend films. When the blends consisted of PS and DPS with the same molecular weight, DPS segregated to the free surface after annealing. Moreover, the extent of surface segregation increased when the annealing time, the film thickness of the blends, and the molecular weight of the polymers in the blends were increased. When blends contained PS and DPS with different molecular weights, DPS always segregated to the free surface as long as PS had molecular weights that were greater than DPS. However, PS segregated to the surface when PS had a relatively small molecular weight, indicating that the surface free energy of polymers, which caused surface segregation in blends of PS and DPS, was determined by both molecular weight and isotopic effects.