In the title compound, [Fe(C(5)H(5))(C(17)H(15)N(2)S)], the cyclo-penta-dienyl (Cp) rings are almost parallel and essentially eclipsed, with a dihedral angle between the Cp ring planes of 0.807 (11)°. The Fe atom is slightly closer to the substituted cyclo-penta-dienyl ring, with an Fe-centroid distance of 1.6510 (8) Å, compared with 1.6597 (8) Å for the unsubstituted ring. The bridging unit between the substituted Cp ring and the naphthyl ring system is planar within 0.0174 Å and makes dihedral angles of 59.032 (10) and 66.02 (2)°, respectively, with these two rings. The angle between the substituted Cp ring and the naphthyl ring system is 72.094 (18)°. The H atoms of the NH groups of the thio-urea moiety are positioned anti with respect to each other. In the crystal, mol-ecules form centrosymmetric dimers via pairs of N-H⋯S hydrogen bonds.