Roles of titania layer incorporation and hydrogen peroxide treatment in the preparation of highly dispersed platinum catalysts supported on siliceous SBA-15 mesoporous materials were studied by examining the catalysts at each step of the preparation. XRD, TEM, XPS, Raman, IR, CO chemisorptions, EXAFS and XANES techniques were employed to the investigation of the physico-chemical states of platinum and titanium. The platinum particles were uniformly dispersed on SBA-15 ranged from 1 to 2 nm in size by incorporating titania onto the surface of SBA-15 and then treating the impregnating platinum precursor with hydrogen peroxide, even at platinum loading as high as 4 wt.%. The platinum catalysts showed considerably higher catalytic activity in the combustion reactions of both carbon monoxide and methane, suggesting a suitable catalyst for purifying diesel engine exhaust.