BaTaO2N owns a promising band gap of 1.8 eV and suitable band edge positions but generally exhibits poor photocatalytic activity for water splitting reactions. In this work, we have modified BaTaO2N by introducing Mg to the B site of perovskite lattice to form a new compound, i.e. BaTa0.95Mg0.05O2+xN1-y. This modification results in an alteration to a number of important parameters such as unit cell size, nitrogen content, optical absorption and microstructures etc. More importantly, Mg modifications are responsible for stronger Ta-O/N bonds, lower Ta4+ defects concentration and positively shift of band edge positions, which in turn contribute to high photocatalytic activities for water oxidation reactions. Apparent quantum efficiency as high as 2.59% has been realized at 420 +/- 20 nm, being the highest for BaTaO2N reported to date under similar conditions. Further photoelectrochemical analysis confirms better charge utilizations in Mg modified BaTaO2N. (C) 2020 Elsevier Inc. All rights reserved.