Multiwalled carbon nanotubes (MWCNTs) have wide range of applications. Commercial MWCNTs have impurities, disorder and entangled structure, which limit its applications. In this respect, novel, low-energy consumption and friendly technique was applied to enhance its structure. The technique is operated during isometric process inside autoclave and based on thermal treatment of MWCNTs in the presence of solvent and pressure. It was used to enhance the oxidative thermal stability of MWCNTs. Thermal gravimetric analysis results showed an increase in onset temperature, activation energy of decomposition, and the temperature required to loss 75, 50, and 33 wt% as the treating temperature increased. Raman spectroscopy tests showed a decrease in the degree of disorder from 1.29 for untreated samples to 0.45 for samples treated at 250°C. The electrical resistivity of MWCNTs was increased from 0.33 Ω.cm for untreated samples to 0.54 Ω cm for 250°C treated samples. Advantages of thermal treatment of MWCNTs using this technique appeared in the presence of a percolation behavior for the AC electrical conductivity when a polymer matrix was loaded with it with a threshold percolation concentration of 0.7 wt%. Furthermore, Cole–Cole Z semicircles as well as Argand plots of the electric modulus appeared for polymer matrix loaded with thermally treated MWCNTs beyond the threshold percolation concentration.