Pt nanoparticles with controlled sizes between 1.6-7.0 nm were anchored onto the surface and pores of SBA-15 silica support. The catalysts were characterized by TEM-ED, BET, XRD, and ICP-MS techniques and were tested in liquid phase hydrosilylation of phenylacetylene with triethylsilane. The activity of the 7.0 nm Pt nanoparticles anchored onto the surface of SBA-15 in hydrosilylation (TOF = 0.107 molecules·site −1 ·s −1 ) was~2 times higher compared to the 5.0 nm Pt/SBA-15 (TOF = 0.049 molecules·site −1 ·s −1 ) catalyst and~10 times higher compared to the 1.6 nm Pt/SBA-15 (TOF = 0.017 molecules·site −1 ·s −1 ) catalyst. Regarding the selectivity, bigger nanoparticles produced more vinylsilane-type products (α-and β-(E)-products) and less side products (mainly ditriethylsilane, triethyl(1-phenylethyl)silane and triethyl(phenethyl)silane derived likely from the reduction of the vinylsilane products). However, the selectivity towards the β-(E)-triethyl(styryl)silane was higher in the case of 1.6 nm Pt/SBA-15 catalyst compared to 5.0 nm Pt/SBA-15 and 7.0 nm Pt/SBA-15, respectively, which can be attributed to the beneficial effect of the size differences of the Pt nanoparticles as well as the differences of the quality and quantity of Pt/SiO 2 interfaces.