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 0 -azobis-4-cyanopentanoic acid and the alkylhydroxyl 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.