Magneto-optical polar Kerr effects between 1.5 and 6 eV and the domain structures of body-centered cubic (bcc) FeRh alloy, bcc FeRh0.82Pd 0.18 alloy, and body-centered tetragonal (bet) FeRh0.24Pt0.76 alloy were investigated for the first time. A temperature-induced AF-FM phase transition was attained at a temperature width of 2 K for FeRh and FeRh0.82Pd0.18 alloys at a temperature width of 40 K for FeRh0.24Pt0.76. A large width of the transition for FeRh0.24Pt 0.76 was also observed in the temperature dependence of domain structures investigated by magnetic force microscopy, and may be attributed to the internal stress caused by the anisotropic change in the lattice constants during the transition. The Kerr rotation spectrum of FeRh showed two negative peaks near 2.8 eV and 3.8 eV, which may be due to the contribution of Rh. In the spectrum of Pd-doped FeRh0.82Pd 0.18, a new peak appeared around 4.8 eV and enhanced the rotation. The spectrum of FeRh0.24Pt0.76 alloy resembles that of FePt alloy, and no contribution of Rh is observed.