The support effect on the Pt-Sn-K/Al2O3 Catalysts for the long chain paraffins dehydrogenation to monoolefins has been investigated by the test dehydrogenation reaction of n-octadecane. The catalysts were characterized by using different techniques: BET, MIP, XRD, TEM, SEM, CO-chemisorption, H-2-TPR, H-2-TPD, NH3-TPD and TG-DTA. Results show that the pore structure and the surface characteristic of the alumina supports strongly affect the catalytic performance. The support effect can be divided into three parts: (I) the BET and pore size distribution govern the Pt dispersion of the catalysts, resulting in influencing the dehydrogenation activity; (II) the inherent acidity controls the acidity of the catalysts, bringing on the different product selectivity: (III) the pore volume provides the effective capability for carbon deposition, thus changing the lifetime of the catalysts. These functions should be adjusted for the alumina supports to achieve an optimal catalytic performance. The ideal catalysts were selected to test the lifetime of the catalysts on the dehydrogenation of n-C-16-C-19. High activity (the average conversion is 11.6%) and perfect selectivity (the average selectivity is 92%) were exhibited during the reaction time of 960 h. (C) 2009 Published by Elsevier B.V.