Small-angle neutron scattering is applied to study film-gradient membranes of polyamidoimide and similar membranes, modified by the addition of a fullerene C60 (2 wt %) during phase-inverted sedimentation of the polymer solution. It is demonstrated that membranes without a fullerene have a system of nanoscale pores filling ~20% of the bulk polymer and having a correlation radius of RC ≈ 20 nm. However, the introduction of a fullerene leads to a decrease in the pore size to RC ≈ 15 nm, and their volume fraction decreases by ~40%. In this regard, we discuss the role of fullerenes inclined to the creation of molecular complexes by linking chains, which is important for regulation of the molecular pore structure of membranes.