Magneto-optical Kerr rotation θ K spectra are shown for the amorphous alloy films of R 0 . 3 0 (Fe 0 . 8 9 Co 0 . 1 1 ) 0 . 7 0 with R = La, Pr, Nd, Sm, Eu, Gd, Tb, and Dy, and they are compared with those for R ∼ 0 . 2 Co ∼ 0 . 8 films. On the whole, one of the most remarkable differences is that θ K greatly depends on the species of R for a series of RFeCo in infrared regions, while θ K for RCo scarcely depends on R. This difference is explained by a change in Curie temperature with the R species. Based on this model, spectral subnetwork contributions of R to θ K are estimated. In ultraviolet regions, large negative contributions can be expected for R = Pr, smaller negative ones for Nd and Gd, with large positive ones for R = Tb and Dy, and almost zero for R = Sm.Although experiments are done only on a restricted number of films, the Kerr spectra change only slightly for multilayers from alloy films with corresponding compositions.