The viability of A549 cells, a human lung carcinoma epithelial cell line, was evaluated after exposure to graphene oxide (GO) and its derivatives (dodecylamine GO (DA-GO), reduced GO (rGO), and sodium dodecyl sulfate rGO (SDS-rGO)). A decrease in the relative amounts of C-OH bonds and an increase in the number of C-C and C-N bonds in the C 1s spectra indicated that the reduction of GO to rGO and the surface functionalization of GO has taken place. The appearance of amine stretching bands, out-of-plane C-H stretching vibrations, and S = O stretching bands in the infrared spectra indicated the formation of DA-GO, rGO, and SDS-rGO, respectively. Low concentrations (3-25 µg/mL) of GO, rGO, and SDS-rGO were found to be mildly toxic, whereas DA-GO exhibited severe dose-dependent toxicity over the same concentration range. High concen- trations (50-400 µg/mL) of GO and all its derivatives resulted in severe toxicity to the A549 cells. It is believed that surface functionality strongly affects the viability of A549 cells.