The compositionally modulated FeBSi/Si amorphous films were prepared by rf sputtering. The saturation magnetization of modulated films decreases exponentially with increase of the thickness of Si layers. This is caused by the dead layers. The M?ssbauer spectra measurements showed that the dead layers are the paramagnetic phase formed by the interdiffusion of Fe and Si atoms at the interfaces. The size effect was observed in the FeBSi/Si films. The size effect depends only on the thickness of FeBSi layers, and the dead layer effect depends on both the FeBSi layer thickness and Si layer thickness.