This work investigates the effect of critical properties on aged transformer oil with various additives such as semiconductive nanoparticles, natural and synthetic antioxidants. The additives are added with aged transformer oil in different fraction with the objective to enhance the critical properties of oil and eliminating hazardous disposal. The critical properties like breakdown voltage, flashpoint, firepoint and viscosity of the samples before and after treatment are measured according to IEC and ASTM standards. Impressively it is found that semiconductive nanoparticles, natural and synthetic antioxidants improve the critical properties of aged transformer oil to specified standard. The suitable fraction to which the sample shows constructive result is reported. In addition to that, the above treatment process can be implemented both in the sense of economic retreatment and environmental safety margin.