To improve mean-life and reliability of power cable, we have investigated specific heat (Cp) and thermal conductivity of XLPE insulator and semiconducting materials in 154(kV) underground power transmission cable. Specimens were respectively made of sheet form with EVA, EEA and EBA added $30[wt\%],$ carbon black, and the other was made of sheet form by cutting XLPE insulator in 154(kV) power cable. Specific heat (Cp) and thermal conductivity were measured by DSC (Differential Scanning Calorimetry) and Nano Flash Diffusivity. Specific-heat measurement temperature ranges of XLPE insulator were from $20[^{circ}C];to;90[^{circ}C],$ and the heating rate was $1[^{circ}C/mon].$ And the measurement temperatures of thermal conductivity were $25[^{circ}C],;55[^{circ}C];and;90[^{circ}C].$ In case of semiconducting materials, the measurement temperature ranges of specific heat were from $20[^{circ}C];to;60[^{circ}C],$ and the heating rate was $1[^{circ}C/mon].$ And the measurement temperatures of thermal conductivity were $25[^{circ}C],;55[^{circ}C].$ In addition we measured matrix of semiconducting materials to show formation and growth of carbon black in base resins through the SEM. From these experimental results, both specific heat and thermal conductivity were increased by heating rate because volume of materials was expanded according to rise in temperature.