Mesoporous silica thin films loaded with gold nanoparticles are synthesized in the presence of EO20PO70EO20 (P123). Transmission electron microscope images show that the matrix of the nanocomposite is an ordered porous structure with a two-dimensional hexagonal phase. The wide-angle X-ray diffraction pattern implies that the nanocomposite contains gold crystals. These metallic nanoparticle-embedded solid thin films show some linear and nonlinear optical properties due to their special structure and composition. Gold nanoparticles bring about surface plasmon resonance, and an absorption peak stemming from this effect has been observed. The linear absorption property is analyzed by a quantum mechanism, and the results show that it is in°uenced by the size and volume fraction of gold nanoparticles. Furthermore, it shows an obviously clear nonlinear optical property measured by the z -scan technique. The magnitude of the nonlinear refractive index of the nanocomposite is estimated to be about 10^{-10} cm2/W.