The high-temperature polymorphs of two photocatalytic materials, BiNbO 4 and BiTaO 4 were synthesized by the ceramic method. The crystal structures of these materials were determined by single-crystal X-ray diffraction. BiNbO 4 and BiTaO 4 crystallize into the triclinic system P1¯ (No. 2), with a=5.5376(4)Å, b=7.6184(3)Å, c=7.9324(36)Å, α=102.565(3)°, β=90.143(2)°, γ=92.788 (4)°, V=326.21 (5)Å 3 , Z=4 and a=5.931 (1)Å, b=7.672 (2)Å, c=7.786 (2)Å, α=102.94 (3)°, β=90.04 (3)° γ=93.53 (3)°, V=344.59 (1)Å 3 and Z=4, respectively. The structures along the c-axis, consist of layers of [Bi 2 O 2 ] units separated by puckered sheets of (Nb/Ta)O 6 octahedra. Photocatalytic studies on the degradation of dyes indicate selectivity of BiNbO 4 towards aromatics containing quinonic and azo functional groups.