A series of Pt-Sn/SBA-15 catalysts (Sn/Pt nominal ratios: 0-3) prepared by direct reduction were applied to ethylbenzene dehydrogenation to styrene. The characterization by X-ray diffraction, X-ray absorption fine structure, CO adsorption, transmission electron microscopy, and X-ray photoelectron spectroscopy revealed the formation of highly dispersed and stable Pt-Sn alloy particles [PtxSny (x/ y >= 3) and Pt-Sn alloys having Sn-rich surfaces] on SBA-15. Nonalloyed Sn existed as highly dispersed SnO2. 1Pt-1Sn/ SBA-15 (Sn/Pt nominal ratio = 1) exhibited the highest activity, on which Pt3Sn alloy nanoparticles were mainly formed. In contrast, PtSn alloy was dominant on Pt-Sn/SBA-15 catalysts whose Sn/Pt nominal ratios were larger than 1, and the activity was decreased. Furthermore, 1Pt-1Sn/SBA-15 exhibited a higher stability than Pt/SBA-15 and 1Pt-1Sn/SiO2. The addition of Sn not only inhibits C-C bond cleavage and improves selectivity toward styrene but also enhances the "drain-off" effect, allowing coke precursors to migrate from the active metals to SBA-15 with large surface area.