Composite photocatalyst of blue MoO3/g-C3N4 (denoted as MoO3-C3N4) was prepared by a simple mixing-calcination method. The obtained MoO3-C3N4 composite contains a low amount of molybdenum blue and shows remarkably enhanced absorption of visible light and high efficiency for the degradation of methylene blue dye (MB) under visible light. The enhancement of visible light photocatalytic activity in MoO3-C3N4 is attributed to the synergetic effect: (i) the strong and wide absorption of visible light, (ii) the high separation and easy transfer of photogenerated electron-hole pairs at the heterojunction interfaces derived from the match of band position between the g-C3N4 and MoO3. (C) 2015 Elsevier Ltd. All rights reserved.