The properties variation by deterioration of the 600V grade heat-resistant polyvinyl chloride insulated wire(HIV) was analyzed. The weight variation of the thermal deteriorated HIV was about 42% at 80$0^{circ}C$ and over. From the analysis result of the metallurgical microscope photographs it shows that the sorface of normal wire showed the elongated structures. However the elongated structures did not appear at $900^{circ} and over and we could observe that particles were grown. The grown oxidized substances in the thermally deteriorated electric wire were observed by SEM. The CuL, CuK, $CuK_b$, OK and CIK spectra of the thermally deteriorated HIV at $300^{circ}C$ were uniform regardless of the scanning length, but the spectra of CIK could not found at above $700^{circ}. At the DTA analysis, the endothermic reactions were occurred around $3006{circ}C; and; 400^{circ}C$ and the exothermic reactions were occurred around <TEX>$470^{circ}, respectively.