Using a full potential spin-polarized linear muffin-tin orbital band code, we investigate many aspects of the magnetic properties of several FePt multilayers. These include magnetic anisotropy energies, magnetic moments and especially the magneto-optical Kerr effect. We are interested in the variation of the Kerr rotations with composition of the various multilayers and also how these rotations compare to bulk Fe, Pt and FePt. There is experimental evidence that the magneto-optical spectra of FePt alloy films in the L10 structure show strong effects with the onset of ordering. In addition, for the multilayers, we are interested in the variation of the anisotropy energies with composition. Comparison with experimental evidence will be made where permitted.