In this study, mechanical and thermomechanical properties of porous silicone composites with various contents of hollow silica particles, treated by vinyltrimethoxysilane (VTMS) as a silane coupling agent, were investigated using tensile and dynamic mechanical analysis. Series of silicone composites with non-modified hollow silica particles as a reference were also prepared for comparative study. The surface characteristics of VTMS-modified hollow silica particles were analyzed using FT-IR spectroscopy. The vinyl function groups on VTMS-modified hollow silica particles led to a chemical bonding to silicone matrix, resulting in reinforcing the mechanical properties of the silicone composites. Tensile modulus of porous silicone composites without the surface modification of silica particles could be predicted by Einstein and Guth/Gold equations, implying the hydrodynamic reinforcement contribution. On the other hand, considerable improvement in the tensile modulus of silicone composites was achieved by strong interfacial adhesion created by chemical bonding on the surface of VTMS-modified hollow silica particles.