Four novel polytantalotungstates K5Na4[P2W15O59 (TaO2)(3)]center dot 17H(2)O(1), K8Na8H4[P8W60Ta12(H2O)(4)(OH)(8)O-236]center dot 42H(2)O(2), Cs3K3.5H0.5[SiW9(TaO2)(3)O-37]center dot 9H(2)O(3), and Cs10.5K4H5.5[Ta4O6(SiW9Ta3O40)(4)]center dot 30H(2)O(4) were synthesized. Compounds 1 and 3 are tris-(peroxotantalum)-substituted Dawson- and Keggin-type derivatives, whereas 2 and 4 are teerameric oligomers containing respectively an unprecedented {Ta-12} and {Ta-16} cluster core. The photocatalytic activities of 2 and 4 for H-2 evolution from water were evaluated. The significantly enhanced performance against the control K-6 [P2W18O62] can be attributed to the modulation of the electronic structures of these novel POMs by Ta incorporation. The highest activity observed so far with the use of 2 can be further rationalized by the presence of distorted heptacoordinate Ta atoms in the form of TaO7 pentagonal bipyramid.