The photocatalytic potential of a derivative family of the Keplerate type nano-porous Mo–O based polyoxometalates with general formula [Mo₇₂^VIMo₆₀^VO₃₇₂(L)₃₀(H₂O)₇₂]ⁿ⁻ (L = CH₃COO⁻, SO₄²⁻) (denoted Mo₁₃₂) has been evaluated by a prototype photocatalytic decoloration reaction of aqueous rhodamine B. The Mo₁₃₂ anions are found to be photocatalytically active centers, however they are unstable and subjected to decomposition in the solution form. The introduction of organic counter cations such as tetrabutylammonium (n-Bu₄N⁺) and dioctadecyldimethylammonium (DODA⁺) can endow significant stability to the giant anions during the catalytic process. TOC changes and GC/MS measurements were done to identify the degradation products. Among the derivatives, compound 2 composed of n-Bu₄N⁺ and Mo₁₃₂ (L = CH₃COO⁻) has been found to be the most active one towards the photocatalytic decoloration of RhB solution. The analytical mechanism indicates that both OH radicals and ¹O₂ participate in the photo degradation process.