Hollow silica spheres were synthesized by template/Sol-Gel approach, using cationic polystyrene (PS) as template and tetraethoxysilane (TEOS) as precursor. The void size of hollow silica sphere was decided by the diameter of their PS templates. Hollow silica spheres with controllable size between 0.71 mu m and 1.8 mu m were obtained by varying the parameters of polymerization (the monomer, the initiator, the stabilizer and the polarity of the dispersion medium). The shell thickness of hollow silica spheres could be easily changed in the range of 20 nm to 60 nm by changing the TEOS concentration from 0.4 mmol/L to 0.8 mmol/L. Both the size and shell thickness of hollow silica spheres have effects on their bulk density, the thermal conductivity and strength of materials.