The goal of this study is to understand reactions of acids with single-walled carbon nanotubes (SWCNTs). The SWCNTs were carboxylic acid functionalized via reflux with inorganic and organic acids. The experimental approach involved studying infrared and UV/visible spectra to see if the SWCNTs were indeed functionalized, as well as measuring change in surface area with a surface area analyzer to show the degree of functionalization. The results revealed that several functional groups were introduced, including alkane and carbonyl groups. The carbonyl groups are most likely carboxylic acids, as shown by the peaks in the infrared spectra. These results indicate that not only inorganic, but also organic acids can lead to oxidation of the SWCNTs.