This paper describes the carbonization characteristics of a phenolic resin deteriorated by tracking under the environment of a fire. In the experiment, a liquids droplet of 1[％] NaCl was dripped on the phenolic resin to cause a tracking with 110[V], 220[V] voltages applied. It can be addressed from the experimental results that when an insulator is carbonized by an external fire, its structure is amorphous. If an insulator is carbonized by electrical cause, on the other hand, its structure would be crystalline. In order to observe the surface change of the phenolic resin, the tracking process was analyzed by using SEM. In the case that the materials are carbonized under heat or fire, the exothermic peak appears around 500[$^{circ}C$]. This is one of the important factors to determine the cause of fires. As a result of DTA, the exothermic peaks of an untreated sample showed at 333.4[$^{circ}C$], 495.7[$^{circ}C$] but those of a sample deteriorated by tracking appeared at 430.6[$^{circ}C$], 457.6[$^{circ}C$] in a voltage of 110[V], and at 456.2[$^{circ}C$], 619.7[$^{circ}C$] in a voltage of 220[V]. It is possible, therefore, to distinguish a virgin sample from carbonized samples(graphite) by the exothermic peak.