Functionalized MWNTs have been of interest for dispersion enhancement in processing or for chemical modifications. Modification of multiwall carbon nanotubes (MWNTs) by ultrasonication with oxidizing acid mixtures is frequently used to functionalize CNTs. In this work, the functionalization process of MWCNTs involves using a mixture of concentrated sulfuric acid and nitric acid (95% H2SO4: 65%HNO3, 3:1 volume ratio), ultrasonicated at 250C for 30min. The results confirmed by Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). From the FTIR spectrum, the existence of carboxyl group indicates the functionalization of MWCNTs on the outer surface wall. SEM micrographs show the occurrence of surface modification on the MWCNTs structure. Finally, a well dispersed of MWCNTs colloidal was successfully obtained with less MWCNTs structure collapsed.