A series of Ni_xSiO_2(1-x) granular films were made by a magnetron rf sputtering system with variation of x and the annealing process. Both the complex dielectric function and magneto-optical polar Kerr spectra of the samples were me asured at room temperature in the 1.5～4.5eV photon energy range, respectively. I t was found that there are new spectral features in the dielectric functions. The ε1 spectra change continuously from positive to negative at the low photon energy range in these metal-insulator granular films by adjusing the composition or by the annealing process. For the Ni_xSiO_2(1-x) samples, there are broad peaks in the Kerr rotation and ellipticity spectra. The Kerr in tensities increase with increasing Ni composition. Both the off-diagonal terms of the dielectric terms tensor and optical constants play important role in th e enhancement of the Kerr effect in a particular spectral range for the metal-i nsulator granular films.