An extensive study of the magnetic and magneto-optical properties for NdxFe100-x, PrxFe100-xand Nd40- Fe51Co6Ti3amorphous films synthesized by r.f. sputtering onto heated substrates has been carried out. Both Nd-Fe and Pr-Fe alloy films exhibit the maximum values of the perpendicular magnetic anisotropy constant Kuat 300K at about 40 at% of Nd and Pr elements. The strong thickness dependence of Kuwas found in both Nd40Fe51- Co6Ti3and Pr40Fe60films fabricated at the substrate deposition temperature C. The Kerr rotation angle θKincreases with decreasing wavelength in the range from 350 to 800 nm in those alloy films with Nd and Pr. This trend is in contrast to that of films with heavy rare earths. Together with observation by high resolution electron microscopy, it is proposed that a short range atomic ordering in a microcrystalline amorphous structure plays an important role in the perpendicular magnetic anisotropy mechanism.