In this work, black titanium monoxide (TiO) nanoparticles were synthesized by hydrogen assisted magnesium thermal reduction method from nanotube titanic acid (NTA) and their electromagnetic properties were investigated. The black TiO nanoparticles exhibited the optimal reflection loss of-37.7 dB at a thin absorbance layer of 1.2 mm in thickness, which showing a promising candidate in electromagnetic wave absorbing (EA). To explore the mechanism of EA, TiO nanoparticles prepared from the other two initiators (commercial grade TiO and P25 titanium dioxide) was used as a comparison. The results show that the crystalline structure and microscopic defects, which arouse from the formation of TiO in the hydrogen assisted process, affect the electromagnetic performance of Ti-O binary system significantly in addition to their intrinsic effects. We hope this study help to open a new way for the designing of highperformance EA materials. (c) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.