The nanostructures of fibrillar organogels made from complex triamide and tetramide were investigated by small-angle X-ray and neutron scattering. In the explored concentration c-range and scattering vector q-range, it is mainly the form factors of the fibers that are measured and information about the average shape of their cross section that is gained. The fibers were found to have a cross section of characteristic average size close to 80 Angstrom and a crystalline internal structure. However, they can be considered as homogeneous particles for a spatial resolution of 20 Angstrom, as shown by using the contrast variation method with neutron scattering. Eventually, the q-dependence of the form factors in the Porod limit can be accounted only by introducing anisotropy in the cross section shape. For the tetramer, this anisotropy was in agreement with the crystalline order of the fibers observed in the solid state.