We report the tunable conductivity of single walled carbon nanotubes and multi-walled carbon nanotubes with their surface walls decorated by Gold nanoparticles in the elusive THz frequency range (0.3-2.0 THz). Colloidal gold nanoparticles were synthesized by the reduction of gold chloride solution using tri-sodium citrate. A simple chemical route is followed to attach Au NP on the surfaces of carbon nanotubes. THz conductivity spectra are explained with the help of modified Universal Dielectric Response model.