We have investigated the magnetic and magneto-optic properties of the compositionally modulated Co/Pt multilayers by a magneto-optic Kerr spectometer using photoelastic modulator. The samples were prepared by an e-beam evaporation technique. We have used a magneto-optic Kerr spectrometer which could measure the Kerr rotation angle in the wavelength range of 300 nm - 800 nm with a maximum applied magnetic field of ±18 kOe. The Kerr spectrometer could measure the Kerr rotation angle up to ±5˚ with a 0.001˚ resolution. We could get the Kerr hysteresis loops with a maximum applied field of 18 kOe at any wavelength between 300 nm and 800 nm which could provide the informations about the coercivity, the magnetic anisotropy, and the magnetic domain structure. We have found that the multilayer structure composed of less than 4-Å Co and more than 6.9-Å Pt is appropriate magneto-optic recording material for its large Kerr rotation angle and 100% remanence at room temperature.