Sillenite-type Bi 25 GaO 39 as an efficient photocatalyst was studied in the present paper. The compound synthesized by a solid state reaction method has a band gap of 2.95eV. It possesses a fair visible-light-response ability. The UV-light-induced photocatalytic activities for degrading methylene blue follow the decreasing order of anatase TiO 2 >Bi 25 GaO 39 >Bi 12 GeO 20 >Bi 24 Ga 2 O 39 , different from Bi 12 GeO 20 >Bi 25 GaO 39 >Bi 24 Ga 2 O 39 >TiO 2 under visible light irradiation. The dispersion of Pt over Bi 25 GaO 39 leads to an obvious increase in photocatalytic performance. The opener structure of Bi 25 GaO 39 is proposed to explain the higher UV-light-induced photocatalytic activity, compared with Bi 24 Ga 2 O 39 and Bi 12 GeO 20 .