Ketalization reaction, which is otherwise a typical acid catalyzed process, is herein firstly realized by a novel visible light driven photocatalytic reaction system with methylviologen (MV2+) as an efficient electron mediator and graphitic carbon nitride (g-C3N4) as the visible light sensitizer. The photons utilization efficiency of g-C3N4 was maximized by simultaneous removal of the conduction band electrons and valence band holes by MV2+ and methanol, respectively. The turn over number of MV2+ reaches the remarkable high value of 31201/hour, with 72.7 mmol of cyclohexanone dimethyl ketal production in 1 h. The design strategy presented in this work could inspire the development of new and highly efficient photocatalytic reaction systems for broader purposes than usually expected. (C) 2017 Elsevier B.V. All rights reserved.