Nano-composite based on multiwall carbon nanotubes (MWCNT), modified with polyaniline was prepared by in-situ oxidation polymerization method of aniline monomer in the presence of functionalized MWCNT. The prepared PANI/MWCNT is investigated by several techniques including microstructure characterizations using scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM). Then subjected to X-ray diffraction (XRD) and then examined with Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The XRD pattern reflects the high purity of the PANI/MWCNT composite and the low crystallinity which is attributed to the high molecular weight of polyaniline. The HR-TEM revels that the MWCNT were uniformly decorated with spherical PANI nanoparticles with nearly no agglomeration. The co-operative behavior between MWCNTs and PANI gives rise to the production of advanced functional materials with a wide range of applications.