In the title heteronuclear Ni(II)-Ho(III) complex (systematic name: {μ-6,6'-dieth-oxy-2,2'-[ethane-1,2-diylbis(nitrilo-methyl-idyne)]diphenolato-1κ(4)O(1),O(1'),O(6),O(6'):2κ(4)O(1),N,N',O(1')}trinitrato-1κ(6)O,O'-holmium(III)nickel(II)), [HoNi(C(20)H(22)N(2)O(4))(NO(3))(3)], with the hexa-dentate Schiff base compartmental ligand N,N'-bis-(3-ethoxy-salicyl-idene)ethyl-enediamine (H(2)L), the Ho and Ni atoms are doubly bridged by two phenolate O atoms of the Schiff base ligand. The coordination of Ni is square-planar with the donor centers of two imine N atoms and two phenolate O atoms. The holmium(III) center has a tenfold -coordination environment of O atoms, involving the phenolate O atoms, two eth-oxy O atoms and two O atoms each from the three nitrates. Weak C-H⋯O and O⋯Ni [3.383 (4) Å] inter-actions generate a two-dimensional zigzag sheet.