Potassium Niobate was obtained by grinding the mixture of niobium formate and potassium hydroxide and small amount of water, then dried at room temperature, and finally calcined at 500 ℃ for 3 h . It can be seen from the Infrared spectroscopy that an ionexchange reaction occurred and NH3 was released during grinding. Assynthesized potassium niobate powders were used to degrade methylene blue solution under irradiation of UV, and found that the catalyst showed better photocatalytic properties, and the degradation ratio reaches to 90% after 3 h reaction.