[en] The magneto-optical Kerr spectra in PtMnSb, MnBi, and MnPt3 were calculated by the first-principles LMTOASA method. These three materials have large Kerr rotation angles of about 1-2 degrees in a low-energy region around 1-2 eV. The large Kerr rotation peaks of the three materials are compared and discussed in detail. (author)