New layered compounds, A(4)Ta(x)Nb(6-x)O(17) (A = K or Rb, x = 2, 3, 4 and 6), which had two different kinds of interlayer spaces were prepared. It was found that these compounds with intercalated nickel metal particles showed a marked photocatalytic activity for an overall water splitting. The rate of H-2 and O-2 evolution on Ni-Rb4Ta6O17 was smaller than that on Ni-Rb4Nb6O17 because Rb4Ta6O17 had a larger band gap than that of Rb4Nb6O17. The quantum efficiencies (<250 nm) for both materials were, however, almost the same. In the case of Ni-K4TaxNb6-xO17, the rate of H-2 and O-2 evolution decreased with the increase of Ta substitution though the threshold of UV absorption shifted to longer wavelength, suggesting that the extended absorption to a longer wavelength did not contribute to the photocatalytic water splitting. It was also found that A(4)Ta(x)Nb(6-x)O(17) itself without any modification could decompose water, which confirmed that the structure consisting of two different kinds of interlayer spaces is essential for water splitting.