The reactions of 3,3′-bis(5-mercapto-1,2,4-triazole) with Co(II) and Ni(II) ions, respectively, gave two nanospheric mixed-valence icosanuclear cage-like complexes [M₂₀L₁₂](SO₄)₂·6DMF·CH₃OH·3H₂O (M = Co, 1; Ni, 2) with the in situ generated oxalyldithiosemicarbazide (H₄L) as ligand. The eight octahedral M(II) ions and twelve square-planar M(III) ions in the two complexes are linked by twelve three-connecting linkers of L⁴⁻ to build an icosanuclear [M^II₈M^III₁₂L₁₂]⁴⁺ nanocage with an inner cubic M^II₈ cage core. Their cage skeletons are stable in water. The sulphate anions reside over the cage portals. The magnetic measurements of the two complexes revealed the presence of dominant antiferromagnetic interactions between the metal ions in both complexes.