The breakdown mechanism of electrical insulator used at higher temperatures above room temperatures is generally affected by thermal degradation. This paper describes the effects of temperature on AC dielectric breakdown properties of DGEBA/MDA/SN system of which impact strength is improved by the addition of SN(succinonitrile). The dielectric breakdown strength decreased with increasing temperature which may be due to expansion of space charge and electric field relaxation around needle tip. The dendrite type tree of dense branched was observed by cutting the chain due to iterative electrical stress then initiation and propagation of electrical tree from the top of specimen needle were occurred.