Substitution effects of Ta5+ by Nb5+ in BiTa1-x Nbx O4 (0≤x≤1.0) on photocatalytic, photophysical,and structural properties were in investigatd. The powder x-ray diffrction and Rietveld structural refinement showed that the structure of BiTa1-x Nbx O4 at R=at R=0.2, 0.8, and 1.0 is an orthorhombic system with space goup pnna. Ultraviolet-visble diffuse reflectance spectroscopy measuremetnt revealed that the band agp of orthorhombic samples is narrower than that of triclnic compounds. The H2 Bi Ta1-xNbxO4 under ultraviolet irradiation. The orthorhombic compound at R=0.2 showed the highest activity. which is higher than that of the well-known TiO3 photocatalyst.