The development of new synthetic pathways to assemble novel 3d-4f heterometallic nanoclusters is a considerable challenge. Incorporating lanthanide ions that play a special role in the field of single-molecule magnetism in such molecular clusters provides good starting ingredients for the syntheses of 3d/4f single-molecule magnets. In continuation of our research on the construction of heterometallic 3d-4f clusters [1] we present herein an appealing route for the synthesis of Mn-Tb/Ho nanoclusters with the highest-nuclearity known by today from a smaller hexanuclear {Mn6} isobutyrate precursor. Two new mixed-valent heterometallic dotriacontanuclear MnII,III-LnIII coordination nanoclusters [Mn26Ln6O16(OH)12(O2CCH(CH3)2)42] (LnIII = Tb (1), Ho (2)) with ca. 3.4 x 1.8 nm size have been synthesized and characterized by IR spectroscopy and X-ray diffraction analysis. The compounds are isostructural and crystallize in the orthorhombic space group Pnna with a = 28.177(1), b = 58.315(1), c = 16.089(1) Å, Z = 4, V = 26437(1) Å3 (1) and a = 28.297(1), b = 58.583(1), c = 15.948(1) Å, Z = 4, V = 26437(1) Å3 (2). The clusters reside on two-fold rotation axes and possess C2 molecular symmetry. They comprise a [MnII10MnIII16LnIII6]86+ core, bridged by fourteen μ4-O, two μ3-O, twelve OH groups, and encapsulated by forty-two bridging isobutyrate moieties (Figures 1). Charge consideration of clusters 1 and 2 and BVS calculations indicate that 16 Mn centers are in the +3 oxidation state (Mn1, Mn2, Mn4, Mn5, Mn7, Mn8, Mn10 and Mn12), whereas the remaining 10 Mn centres are in the +2 oxidation state (Mn3, Mn6, Mn9, Mn11 and Mn13). Interestingly, Mn atoms are six-coordinated while Dy atoms are either eight- or nine-coordinated in 1 and 2. Magnetic studies reveal that 1 exhibits single-molecule characteristics up to 12 K.  Figure 1. Structure of [Mn26Tb6O16(OH)12(O2CCH(CH3)2)42] cluster. Methyl groups and H atoms are omitted for clarity.