Multi-walled carbon nanotubes (MWCNTs) were chemically functionalized by using sulfuric acid and nitric acid. The functionalization was done with two different acid ratio. The functionalized nanotubes were characterized with Fourier Transform Infrared Spectroscopy, X-Ray Photon Spectroscopy, Thermal Gravimetric Analysis, Elemental Analysis, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy. Sulfonation of carbon nanotubes (CN) increased the electrical conductivity of carbon nanotubes up to 1.25 x 10-1 S/cm. The SEM micrographs of the samples showed that CN was observed in more bulky form due to the increasing hyrogen bonding between the particles. The zeta potential of the CN increased with increasing sulfonation amount.