In the power generation, transmission or distribution of electricity, transformer is one of the most valuable and important asset. The transformer reliability is very dependent on the quality of the insulation system. During the operational phase transformer, transformer oil will undergo degradation or deterioration due to high temperatures and chemical reactions that occur as oxidation. Aging in insulating oils would also affect its characteristics, such as physical and electrical properties, as well as lowering the lifetime of the insulation. This paper discusses the aging of insulation oil. Research on accelerated thermal aging was conducted to determine the behavior of insulating oil deterioration Nynas Nytro 10X and predict future use. Based on the Arrhenius law, if the temperature of transformer oil samples were operating normally in 60°C, the lifetime prediction of insulating oil will be 697.079 hours. Furthermore, the percentage decrease in the lifetime prediction isolation transformer IBT CBN S phase at normal loading conditions, the imposition of emergency at long time, as well as the emergency at short time in a row at 0.002032%, 0.047435% and 0.957268% of the rest period normal to the insulation of 5.5 years.