EPDM is the most commonly used type of rubbers for cables insulation. In order to improve the EPDM insulation rubber performance, many additives can be used. Aluminum hydroxide is used as a fire retardant because it is safe and cheap and reduces the amount of smoke produced in fires. In this study, two concentrations (10 and 20 phr) of aluminum hydroxide ATH were used to improve EPDM insulation properties and to prolong its operational life. The effect of gamma doses (up to 600 KGy) on the mechanical, physical and thermal properties of EPDM/ ATH has been investigated. The results of the present study show that the optimum concentration of ATH is 20phr.