We present an innovative concept for the design of electrorheological fluids (ERF) based on a dispersed phase of rigid-rod-shaped metallo-supramolecular polyelectrolytes (MEPE) intercalated in mesoporous SBA-15 silica. While applying an electric field to this composite dispersed in silicone oil, rheological measurements reveal a strong increase in the storage modulus, indicating the solidification of the fluid. Besides the strong electrorheological effect and the low current densities, we note that the required amount of MEPE is five times lower than in comparable host-guest ERFs. Composites based on mononuclear complexes do not show a comparable electrorheological effect.