A new bimetallic complex containing a 4'-ferrocenyl-(2,2':6',2''-terpyridine)palladium core with polyethylene glycol-based pyridine is applied in seeded-growth self-assembled supramolecular polymerization, which affords nanoribbons with controllable lengths and the process follows a first-order reaction kinetics. This approach is successfully demonstrated for a bimetallic organic complex for the first time.