Four novel tri- or tetranuclear organolanthanide metallomacrocycles [Cp(2)Ln(mu-Im)(THF)(3) (Cp = C5H5, Ln = Yb (1), Er (2)], [Cp2Dy(mu-Im)](4)(THF)](3)center dot 2THF (3), and [Cp'Yb-2(mu-eta(1):eta(2)-Tz)](4)center dot 2THF (Cp' = CH3C5H4) (4) have been synthesized through protolysis of Cp(3)Ln or Cp'Yb-3 with imidazole or triazole, indicating that both the bridge-ligand size and the lanthanide-ion radii can be applied in the modulation of the metallomacrocycles. Further investigations on the reactivity of complexes 1, 3, and 4 toward phenyl isocyanate reveal that PhNCO inserts readily into the simple bridge Ln-N bonds of 1 and 3 to yield the corresponding insertion products [Cp(2)Ln(mu-eta(1):eta(2)-OC(Im)NPh)](3) (Ln = Yb (5), Dy (6)) but cannot insert into the Ln-N bond with a mu-eta(1):eta(2)-bonding mode in 4. The novel bridge ligand [OC(Im)NPh] can expand the numbers of the ring members from 12 to 18 in 5 or 16 to 18 in 6. The number of metal atoms in the metallacycles with the ligand [OC(Im)NPh] is independent of the lanthanide-ion size; both trinuclear lanthanide macrocycles are observed in 5 and 6. All of these new complexes have been characterized by elemental analysis and spectroscopic properties, and their structures have also been determined through X-ray single-crystal diffraction analysis.