Electron diffraction technique was used to study the structure of various amorphous films of Gd-Co alloy and Lorentz electron microscopy was used to observe the related magnetic structure. Seven halos could be seen clearly in all the electron diffraction patterns obtained and the two smallest halos were located in the range s-1 (s = (2sinθ)/λ). Magnetic bubbles or in-plane domain structures wereobserved in these amorphous films. For amorphous alloys of this type consisting of two elements, such as rare-earth and transition metals with a large difference in atomic radius, we showed how to derive directly and qualitatively the relative co-ordination number of nearest neighbours between rare-earth metal atoms, - between transition metal atoms, and between rare-earth and transition metal atoms, merely from the diffraction intensity profiles in the range s-1. The influence of phase separation in the film on the magnetic anisotropy was also discussed.