Abstract: The effect of Sn promoter on the performance of Pt-Sn/γ-Al₂O₃ catalysts for the long-chain paraffins dehydrogenation to monoolefins was studied by n-dodecane dehydrogenation. The catalysts were characterized by N2 adsorption-desorption, mercury intrusion porosimetry, CO pulse chemisorption, X-ray photoelectron spectroscopy and thermogravimetric analysis. Results show that the Pt-Sn/γ-Al₂O₃ catalysts exhibit the optimal catalytic performance when the Sn∶Pt (atomic ratio) of the catalyst is 3. While keeping on increasing the amount of Sn, the catalytic dehydrogenation activity of the catalysts is decreased with the formation of Sn0 and Pt-Sn alloy. Moreover, the catalytic stability of the catalysts is enhanced after the addition of Sn. And with the increasing of Sn loading, the selectivity to mono-olefins of the Pt-based γ-Al₂O₃ catalysts is also greatly increased.