Polyoxometalates (POMs) are early transition metal (M = V, Nb, Ta, Mo and W in their highest oxidation state) oxygen anion clusters. Several classes of POMs have been reported to have potent anti-tumor, anti-viral and anti-bacterial properties, resulting in a substantial interest in the potential medicinal application of POMs. Several studies were recently made on the hydrolysis of DNA- and RNA-model substrates by using the isopolyoxometalates [Mo7O246-]1 as well as a Zr(IV)-substituted Wells-Dawson type POM2 as artificial phosphatases. Phosphodiester bonds form the backbone of DNA and RNA macromolecules and are extremely resistant towards hydrolysis. The half-life for spontaneous phosphoester bond hydrolysis has been estimated to be higher than 100 000 years for DNA and 4 years for RNA at neutral pH and 25 °C. Despite the extreme stability of the phosphoester bond, its efficient cleavage is a required procedure in biochemical fields. In nature phosphatases are responsible for hydrolyzing phosphodiester bonds with impressive rate enhancements. In our quest to understand the biological role of POM anions on a molecular level, the phosphoesterase activity of a bimetal-substituted [α-PW11O39]7- Keggin type POM is examined.