The thin film diffusion couples of rare earth and transition metal (RE-TM) (RE = Ce, Er and Tm = Fe, Co) were prepared by electron beam deposition at water cooled temperature. The solid state amorphization reactions have been confirmed by X-ray diffraction in the as-deposited CeFe, CeCo and ErCo multilayers but not for ErFe. Anomalous fast diffusion was observed in the CeFe and CeCo as-deposited diffusion couples by means of RBS. On the other hand, very little diffusion occurs in the ErFe and ErCo cases. Those results indicate that cerium has a unique property allowing transition metals to diffuse extremely fast. Also, cerium exhibits a special high amorphous formability in the RE-TM diffusion couples while very low for erbium. Amorphous formability of cobalt is also higher than iron.