A nitride etching method by oxygen plasma using hydrogen implantation effect is reported. High-resolution patterning of nitride film with sub 50 nm width is demonstrated using this etching method. The mechanism of the nitride etching process has been investigated with various measurements in this study. The measurement results show that the binding of nitrogen and hydrogen in the nitride films is caused by the irradiation of hydrogen-containing gas plasma and the hydrogen implantation into the nitride film plays an important role in the nitride etching by oxygen plasma. No plasma-induced damage in nitride film, such as formation of defects and dislocations, is observed in the case that this etching method is used. This etching method with low damage is applicable to the fabrication of various nitride-based devices.