Research on cobaltferrite based composites has increased recently due to their potential applications such as noncontact magnetoelastic stress or torque sensors and erasable magneto-optic recording media. We report a study of the polar Kerr rotation spectra for CoFe2−xGaxO4 (with x=0.4 and x=0.8). Each of the spectra consists of two peaks of negative Kerr rotation in the measured photon energy range of 1.5–3.0eV. For x=0.4, one peak occured at 1.8eV and the other at 2.25eV. For x=0.8, the first peak shifted to a higher energy of about 1.9eV, while the second peak remained at 2.25eV. The origin of the peaks in the polar Kerr spectra and the observed shift of peak position resulting from Ga substitution can be explained by the intervalence charge-transfer transition, in which an electron from a metallic cation is transferred to a neighboring cation through an optical excitation.