The bulk glass transition temperature, T-g(b), of miscible binary blends can be well expressed by the Gordon-Taylor equation. Extending this notion to surface, the surface composition in the blend would be obtained by measuring the surface glass transition temperature, T-g(g), of each constituent as well as their blend. The most intriguing advantage of this technique is that labeling of a component is not necessary, unlike conventional spectroscopy. To confirm the validity of our technique, the surface composition in a mixture of polystyrene (PS) and deuterated PS (dPS) was evaluated and compared with the results by well-established surface characterization techniques, static secondary ion mass spectroscopy, and neutron reflectivity. They were in good accordance with one another within the experimental accuracy. Hence, it was claimed that the proposed method was powerful to study the surface concentration in miscible binary blends. Finally, the surface composition in blend films of two PSs with different molecular weights was experimentally and systematically elucidated. The surface enrichment of a smaller molecular weight component became more remarkable with increasing molecular weight disparity between the two components due to an entropic effect.