Two new compounds, LiBi4Nb3O,4 and LiBi4Ta3O,4, have been synthesized by the solid-state method, using Li2CO3, Bi2O3, and M2O5 (M = Nb, Ta) in stoichiometric quantities. These compounds crystallize in the monoclinic C2/c space group with a = 13.035(3)angstrom, b = 7.647(2) angstrom, c = 12.217(3)angstrom, beta = 101.512(4), V = 1193.4(5)angstrom(3), and Z = 4 and a = 13.016(2)angstrom, b = 7.583(1)angstrom, c = 12.226(2)angstrom, beta = 101.477(3), V = 1182.6(5)angstrom(3), and Z = 4, respectively. These are isostructural and the structure along the b axis consists of layers of [Bi2O2](2+) units separated by layers of LiO4 tetrahedra and NbO6 octahedra hence depicting an unusual variation in the Aurivillius phase isolated for the first time. The presence of lithium has been confirmed by Li-7 NMR studies. ac impedance measurements and variable temperature Li-7 NMR studies indicate oxygen ion conductivity in these materials. The UV-visible spectra suggest a band gap of 3.0 eV for LiBi4Nb3O14 and 3.5 eV for LiBi4Ta3O14, respectively, and the associated studies on degradation of dyes and phenols render these materials suitable for photocatalysis.