A family of ceramic compounds with general formula of Bi2MNbO7 (M = In, Al, Fe, Sm) were prepared by both processes of sol-gel and solidstate reaction. The resulting fresh gels were subjected to different heat treaments at 200, 400, 600 and 800 degrees C for 4 h. Reaction products were characterized by X-ray diffraction (XRD), thermal analysis (DTA-TGA), specific surface area (using BET method), UV-Vis and FT-IR. Sol-gel technique has many advantages compared to the conventional methods in preparing raw materials and catalysts. Photocatalytic activity of each compound was determined, by testing them in the degradation reaction of methylene blue at room temperature. The decomposition rate was calculated applying the Langmuir-Hinshelwood model. We have found that photocatalytic activity is favored when the structure of each compound has not been formed. According to the t(1/2) (half life) and k (kinetic constants) values, samples of Bi2FeNbO7 sol-gel treated at 400 degrees C presented the highest photocatalytic activity. Photodegradation of methylene blue showed that the photocatalysts obtained by the sol-gel method exhibited higher activity than those prepared by solid state reaction and also higer than the well-know TiO2 (Degussa P-25) photocatalyst. At low temperature such as 400 degrees C, crystalline phases were not detected in any of the componds prepared by sol-gel method.