Boron-rich alloy boron suboxide (B6O) as a novel metal-free photocatalyst was recently explored for photocatalytic CO(2)reduction and water splitting. However, to broaden the potential applications of B6O in the field, further improving its activity and understanding its fundamental chemical properties are essential. Herein, transition metal doping (Cr or Co) is designed to engineer the band structure of B6O via a solid state reaction. The valence band edge of Cr or Co doped B6O is proposed to be more positive than that of pristine B6O while the original conduction band of B6O is not much influenced by doping, contributing to the better light harvesting ability and lower charge recombination rate of doped B6O. The photocatalytic and photoelectrochemical (PEC) performances of doped B6O were therefore remarkably enhanced. The apparent quantum yields (AQY) of 20 wt% Cr or Co doped B6O are much higher than that of pristine B6O. In addition, the 20 wt% Cr doped B6O exhibits the best electrical conductivity and photocatalytic performance compared with the Co doped B6O and pristine B6O. The present work demonstrates a facile and effective strategy to engineer the band structure and reduce the charge migration resistance of B6O. Graphic