Both silica/polystyrene (SiO2/PS) and silica/polystyrene-b-polymethacryloxypropyltrimethoxysilane (SiO2/ PS-b-PMPTS) hybrid nanoparticles were synthesized via surface-initiated atom transfer radical polymerization (SI-ATRP) from SiO2 nanoparticles. The growths of all polymers via ATRP from the SiO2 surfaces were well controlled as demonstrated by the macromolecular characteristics of the grafted chains. Their wettabilities were measured and compared by water contact angle (WCA) and surface roughness. The results show that the nanoparticles possess hydrophobic surface properties. The static WCA of SiO2/PS-b-PMPTS hybrid nanoparticles is smaller than that of SiO2/PS hybrid nanoparticles, meanwhile, the surface roughness of SiO2/PS-b-PMPTS hybrid nanoparticles is yet slightly rougher than that of SiO2/PS hybrid nanoparticles, which shows that the combination and competition of surface chemistry and roughness of a solid material can finally determine its wettability. POLYM. ENG. SCI., 51:218-224, 2011. (C) 2010 Society of Plastics Engineers