Ag-Cu nanocrystal mixture having the molar ratio of 1:1, 1:3, and 1:5 was prepared in thin film SiO2 using the sol-gel method and high temperature heat treatment (500°C). The high resolution TEM micrograph shows the particle size is distributed broadly covering 1-10 nm with the maximum at 4-5 nm. The absorption spectra were simulated using the bulk Ag/Cu dielectric constants by accommodating the nanocrystal size, and were compared with the measured absorption spectra. The third-order nonlinear optical properties of those nanocluster mixtures have been studied by the degenerate four wave mixing technique. The measured third-order nonlinear susceptibilities, χ(3), were on the order of 10-8 - 10-7 esu.