For the development of durable electrochromic (EC) materials with wide absorption, large optical contrast, and high coloration efficiency, a threedimensionally hyperbranched Fe(II)-based metallo-supramolecular polymer (polyFe-3D) was one-step synthesized by the complexation of an Fe(II) salt and an asymmetrical ditopic ligand (L) containing terpyridine (tpy) and phenanthroline (phen) moieties, according to the formation of a 1:2 complex of Fe(II) and tpys (Fetpys) and a 1:3 complex of Fe(II) and phens (Fe-phens). The formation of Fe-tpys and Fe-phens was confirmed by the appearance of two metal-to-ligand charge transfer (MLCT) absorptions in the visible area during the titration experiment. The molecular weight (M w ) of polyFe-3D was determined to 3.96 × 10 5 Da by a size-exclusion chromatography−viscometry measurement. PolyFe-3D with the two different Fe(II) complexes (Fe-typs and Fe-phens) exhibited a pair of redox waves for Fe(II/III) (E 1/2 = 0.74 V vs Ag/Ag + ) reversibly in the cyclic voltammograms. The linear relationship between the peak current and the root of the scan rate during redox suggested a diffusion-controlled redox reaction. The spin-coated polymer film showed reversible EC changes between magenta and pale green, caused by the redox of Fe(II/III). A wide visible region from 430 to 640 nm was covered with the two MLCT absorptions of the Fe-tpys and Fe-phens moieties. The broad MLCT absorption disappeared upon applying 1.2 V vs Ag/Ag + and reappeared at 0 V vs Ag/Ag + . The EC changes were revealed to have both a large transmittance change (ΔT) with 70% at 573 nm and a very high coloration efficiency (η) with 689 cm 2 /C. The coloration efficiency exceeded those of the reported linear (one-dimensional), two-dimensional nanosheeted, and three-dimensional hyperbranched Fe(II)-based metallo-supramolecular polymers. A polyFe-3D film showed high durability for the EC changes of more than 1000 cycles. A solid-state simple device fabricated using polyFe-3D exhibited reversible EC changes of more than 1000 cycles without degradation.