Abstract: Coal tar pitch (CTP) and dioctyl phthalate (DOP) were co-carbonized and the effects of the DOP addition on the thermal behavior of CTP, and the microstructures and electrochemical properties of semi-cokes derived from it were investigated by TGA, polarized light microscopy, SEM, XRD and electrochemical impedance spectroscopy (EIS). Results indicate that the weight loss rates of mixtures of CTP and DOP are slower than that of CTP, indicating that polycondensation between CTP and DOP takes place during co-carbonization. The Lc values of the CTP-DOP cokes are larger while their d₀₀₂ values are smaller than those of the CTP coke. The electrical conductivities of the CTP-DOP cokes are better than that of the CTP coke as revealed by EIS.