The effect of the spatial structure of an interface in multilayer metallic films on the spectrum of x-ray specular scattering is studied. Two types of interface structural defects are considered. One type is steps resulting in a variable layer thickness, and the other is the mixing of unlike metal atoms during epitaxial growth. These defects are shown to have different effects on the specular-scattering spectra. The mixing significantly decreases the Bragg-peak height, especially the height of higher order peaks. The interface roughness results in broadening of the Bragg peaks and in the disappearance of intermediate peaks between them.