Reactive oxygen species (ROS) and activation of redoxsensitive transcription factors such as nuclear factor (NF)-κB have been implicated in pro-inflammatory responses induced by nanoparticles. However, there is still only little knowledge about the pro-inflammatory responses induced by multi-walled carbon nanotubes (MWCNTs). The objective of the present study was to compare the ability of MWCNTs and carbon black (CB) nanoparticles to induce secretion of pro-inflammatory cytokines and to explore possible mechanisms in A549 lung epithelial cells. Exposure of A549 cells to MWCNTs, but not to CB, resulted in a significant increase in interleukin-8 (IL-8) release and gene expression. MWCNTs stimulated NF-κB DNA binding activity, nuclear translocation of the p65 subunit of NF-κB, IkBoc phosphorylation, and ROS generation in A549 cells. MWCNTs-induced IL-8 gene expression and NF-κB activation were abrogated in the presence of ROS scavengers. These results suggest that MWCNTs are able to induce pro-inflammatory responses and NF-κB activation in A549 cells mediated by ROS generation.