The novel layered oxide BiMo2O7OH.2H(2)O was prepared under very mild hydrothermal conditions and the structure determined by ab initio methods from synchrotron X-ray powder diffraction data. The cell is monoclinic, P2(1)/m, Z = 2, with dimensions a = 6.343 21(3) Angstrom, b = 11.597 03(5) Angstrom, c = 5.792 44(3) Angstrom, and beta = 113.329(1)degrees. Refinement using the Rietveld technique converged with R(F)2 = 5.99%, R(p) = 12.67%, R(wp) = 16.92%, and chi(2) = 5.44 for 34 variables and 453 reflections. The structure is composed of infinite chains of edge-shared molybdenyl dimers which are corner-linked along [010]. These are connected via hexacoordinated bismuth atoms to form sheets parallel to (10(1) over bar) which are loosely held together via a hydrogen-bonding network.