Fe/Tb multilayers with various Fe layer thickness and fixed Tb layer thickness were prepared by e-beam alternate vapor deposition. Analyses of the microstructure of these films show that the magnetic performance is strongly affected by the interface structure. Fe in the films evolved to amorphous phase and the Fe/Tb interface became indiscernible with decreasing Fe thickness. At the same time, the film was observed to perform superparamagnetically, which is quite different from the ferromagnetic behavior of Fe/Tb multilayers that have sharp Fe/Tb interface. Our work shows that the interface roughness has strong influence to the properties of magnetic multilayers. Fe / Tb multilayers with various Fe layer thickness and fixed Tb layer thickness were prepared by e-beam alternate vapor deposition. Analyzes of the microstructure of these films show that the magnetic performance is strongly affected by the interface structure. Fe in the films evolved to amorphous phase and the Fe / Tb interface became indiscernible with decreasing Fe thickness. At the same time, the film was observed to perform superparamagnetically, which is quite different from the ferromagnetic behavior of Fe / Tb multilayers that have sharp Fe / Tb interface. work shows that the interface roughness has strong influence to the properties of magnetic multilayers.