The growing use of multi-walled carbon nanotubes (MWCNT) and their derivatives in academic and industrial settings has raised the need to efficiently and accurately determine their potential toxicity in the workplace. Nitrogen-doped multi-walled carbon nanotubes (ND-MWCNT) are modified MWCNT that have enhanced electrical conductivity and are increasingly used in a variety of aerospace and fuel cell applications. Although similar in structure to MWCNT, limited toxicological data is available, and the biocompatibility and mechanism of action of ND-MWCNT have yet to be elucidated. Recent in vivo data showed that NDMWCNT induced inflammation and fibrosis in mouse lungs. In this study, we assess uptake of ND-MWCNT into small airway epithelial cells (SAEC), which may induce molecular toxicological effects. We showed that ND-MWCNT induced higher levels of reactive oxygen species (ROS) in SAEC when compared to their parent MWCNT in short-term in vitro exposure. Treatment of SAEC with low doses (1.2μg/mL) of ND-MWCNT and MWCNT indicated that both induced a significant increase in cell proliferation in a time-dependent manner. Furthermore, significant alterations to the cell cycle were observed in cells treated with both ND-MWCNT and MWCNT in a time- and dose-dependent manner, as shown by an increased percentage of cells in the S and G2 phases of the cell cycle. Confocal images showed alterations in acetylated and total tubulin levels in both ND-MWCNT and MWCNT treated cells as well. Since increases in ROS production and cellular proliferation are associated with multiple pathological conditions, ND-MWCNT exposure may play a role in the initiation of these diseases.