A significant enhancement of critical current density (J c) was obtained in MgB 2 + 3 wt.% glycine samples with a large amount of MgO. The improvements in J c and in the irreversible magnetic field (H irr) are attributed to the pinning effects of high C-substitution level, nanoscale MgO, and to the even boundaries of small grains. This doping method overcomes the degradation of J c under a low field in previously reported SiC-doped samples. Moreover, the formation of MgO was demonstrated to be the result of the reactions between Mg, CO 2 and O 2. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.