Structure of amorphous nangranular composite (Co86Nb12Ta2) x (SiO2)1−x films was studied by means of grazing-incidence small-angle X-ray scattering as a function of atomic concentration x of the metal fraction in vicinity of the percolation threshold. It has been established that the average size of magnetic nanoparticles increases with x and this increment exhibit the anisotropic character. It was found that in a whole concentration range the particles are elongated along the growth direction perpendicular to the film plane. For the lowest concentration x = 0.193, clusters with isotropic shape and average radius of 1 nm were observed, while for higher concentrations up to x = 0.665, the average cluster length along the film normal is 1.5–7 nm and the cross-section is 1–2 nm.