In this article, we present a facile method for the synthesis of an azo-group-bound silica (SiO(2)-azo) initiator. The azo groups were introduced onto the surface of silica (SiO(2)) nanoparticles via facile condensation between 4,4`-azobis-4-cyanopentanoic acid and the alkyl-hydroxyl groups - immobilized on the SiO(2) nanoparticle surface under ambient conditions. The polystyrene (PS) chains were grafted onto the SiO(2) nanoparticle surface by in situ polymerization with the resulting SiO(2)-azo as an initiator, and then, the SiO(2)-PS composite was prepared. The syntheses and properties of the SiO(2)-azo initiator and the composite were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, gel permeation chromatography, and differential scanning calorimetry techniques. The results confirm that the SiO(2)-azo initiator and the composite were synthesized successfully. Styrene was polymerized with the initiation of SiO(2)-azo, and the resulting PS domain accounted for 48.6% of the total amount of composite. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 454-461, 2011