We have successfully prepared composite films of GaAs0.57Sb0.43-SiO2 onto glass substrates by radio frequency magnetron co-sputtering. Microstructure characterization was performed by X-ray diffraction. It is shown that the GaAs0.57Sb0.43 nanocrystals formed and dispersed in the SiO2 matrix. The average size of the nanocrystals was in the range of 3-10 nm. Room temperature transmission absorption spectra of composite films show that the absorption edge exhibits a very large blue shift at approximately 2.25 eV with respect to the corresponding absorption edge in bull;, which is mainly explained by the quantum confinement effect. Room temperature Raman spectra show that the Raman peak of the composite films have a larger red shift than that of the bulk semiconductor due to the phonon confinement and tensile stress effects.