Highly dispersed Pt nanoparticles have been confined in the mesochannels of SBA-15 silica by a simple "one-pot" co-assembly method. Metallic Pt can be encapsulated in the mesochannels by changing the amount of Pt ions in the starting materials. The catalytic performances of Pt-SBA-15 were evaluated for methylcyclohexane dehydrogenation. Compared with conventional supported Pt-SiO2 catalysts, the Pt-SBA-15 catalysts show higher stability. TEM studies show that the confinement effect of ordered mesochannels of SBA-15 may restrict the further growth of Pt nanoparticles during the reaction.