Multiwalled carbon nanotubes (MWCNTs) were functionalized by different functional groups via the Fischer Esterification method. Nitric acid treatment was first used to remove the catalyst from MWCNTs and introduce carboxylic acid groups onto the surface of MWCNTs. These carboxylic groups were used as reaction precursors in the functionalization. Four functional groups-phenol, dodecylamine, 1-octadecanol, and polyethylene glycol-were successfully covalently attached to MWCNTs via amidation or esterification. The functionalized MWCNTs were then characterized by Fourier Transform Infrared (FTIR) spectroscopy, thermal analysis techniques, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The MWCNTs attached to the organofunctional moieties have greater versatility for further utilization in different application fields such as biology, nanocomposites, water treatment, petroleum, and petrochemical technologies.