Thin CuInSi nanocomposite films were prepared by magnetron co-sputtering. The structures of CuInSi nanocomposite films were detected by X-ray diffraction (XRD); XRD studies of the annealed films indicate the presence of CuInSi, a peak at about 2θ=42.400°. The morphology of the film surface was studied by SEM. The nanocrystallization with needle shape of CuInSi could be seen clearly. The grain size is a few hundred angstroms.