In this article, modification of multiwalled carbon nanotubes (MWCNTs) with stearic acid (SA) was done using the wet chemical method. For this aim, MWCNTs were treated with high-concentrated nitric acid to create a functional group as a linkage between MWCNTs and SA. The modified MWCNTs with SA were examined by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), differential scanning calorimeter (DSC), and thermogravimetery analysis (TGA) instruments. The results of TGA and DSC indicate the deposition of about 4.3wt% of SA on the surface of MWCNTs. This proves that the deposition of stearate with a medium diameter size of 20nm on the surface of MWCNTs can be divided into physical and chemical adsorption. As well, the esterification occurs on the surface of functionalized MWCNTs and there is no SA unreacted on the surface of MWCNTs.