In the present study, nitrogen doped carbon nanotubes (N-CNTs) were synthesized using three different aliphatic diamines as nitrogen-carbon precursor solutions with varying carbon chain lengths, in order to elucidate the effect of precursor solution on the overall nitrogen content and ORR activity of the synthesized materials. Increasing the nitrogen to carbon ratio in the precursor solution resulted in higher nitrogen contents in the synthesized N-CNTs, along with enhanced ORR activity for all three samples tested. The increase in activity was attributed to the enhanced properties and edge plane defects of N-CNTs resulting from higher nitrogen contents, illustrating the importance of using a nitrogen rich precursor solution. (C) 2010 Elsevier Ltd. All rights reserved.